diff --git a/docs/pages/api-docs/tree-item.md b/docs/pages/api-docs/tree-item.md
index 69ac352d35e1d7..07764b0d7157a1 100644
--- a/docs/pages/api-docs/tree-item.md
+++ b/docs/pages/api-docs/tree-item.md
@@ -50,10 +50,11 @@ Any other props supplied will be provided to the root element (native element).
 | Rule name | Global class | Description |
 |:-----|:-------------|:------------|
 | <span class="prop-name">root</span> | <span class="prop-name">.MuiTreeItem-root</span> | Styles applied to the root element.
-| <span class="prop-name">expanded</span> | <span class="prop-name">.Mui-expanded</span> | Pseudo-class applied to the root element when expanded.
-| <span class="prop-name">selected</span> | <span class="prop-name">.Mui-selected</span> | Pseudo-class applied to the root element when selected.
 | <span class="prop-name">group</span> | <span class="prop-name">.MuiTreeItem-group</span> | Styles applied to the `role="group"` element.
 | <span class="prop-name">content</span> | <span class="prop-name">.MuiTreeItem-content</span> | Styles applied to the tree node content.
+| <span class="prop-name">expanded</span> | <span class="prop-name">.Mui-expanded</span> | Pseudo-class applied to the content element when expanded.
+| <span class="prop-name">selected</span> | <span class="prop-name">.Mui-selected</span> | Pseudo-class applied to the content element when selected.
+| <span class="prop-name">focused</span> | <span class="prop-name">.Mui-focused</span> | Pseudo-class applied to the content element when focused.
 | <span class="prop-name">iconContainer</span> | <span class="prop-name">.MuiTreeItem-iconContainer</span> | Styles applied to the tree node icon and collapse/expand icon.
 | <span class="prop-name">label</span> | <span class="prop-name">.MuiTreeItem-label</span> | Styles applied to the label element.
 
diff --git a/docs/src/pages/components/tree-view/GmailTreeView.js b/docs/src/pages/components/tree-view/GmailTreeView.js
index c789a46d516762..bc5ec2774e0491 100644
--- a/docs/src/pages/components/tree-view/GmailTreeView.js
+++ b/docs/src/pages/components/tree-view/GmailTreeView.js
@@ -17,16 +17,6 @@ import ArrowRightIcon from '@material-ui/icons/ArrowRight';
 const useTreeItemStyles = makeStyles((theme) => ({
   root: {
     color: theme.palette.text.secondary,
-    '&:hover > $content': {
-      backgroundColor: theme.palette.action.hover,
-    },
-    '&:focus > $content, &$selected > $content': {
-      backgroundColor: `var(--tree-view-bg-color, ${theme.palette.grey[400]})`,
-      color: 'var(--tree-view-color)',
-    },
-    '&:focus > $content $label, &:hover > $content $label, &$selected > $content $label': {
-      backgroundColor: 'transparent',
-    },
   },
   content: {
     color: theme.palette.text.secondary,
@@ -34,9 +24,16 @@ const useTreeItemStyles = makeStyles((theme) => ({
     borderBottomRightRadius: theme.spacing(2),
     paddingRight: theme.spacing(1),
     fontWeight: theme.typography.fontWeightMedium,
-    '$expanded > &': {
+    '&$expanded': {
       fontWeight: theme.typography.fontWeightRegular,
     },
+    '&:hover': {
+      backgroundColor: theme.palette.action.hover,
+    },
+    '&$focused, &$selected, &$selected$focused': {
+      backgroundColor: `var(--tree-view-bg-color, ${theme.palette.action.selected})`,
+      color: 'var(--tree-view-color)',
+    },
   },
   group: {
     marginLeft: 0,
@@ -46,6 +43,7 @@ const useTreeItemStyles = makeStyles((theme) => ({
   },
   expanded: {},
   selected: {},
+  focused: {},
   label: {
     fontWeight: 'inherit',
     color: 'inherit',
@@ -53,7 +51,7 @@ const useTreeItemStyles = makeStyles((theme) => ({
   labelRoot: {
     display: 'flex',
     alignItems: 'center',
-    padding: theme.spacing(0.5, 0),
+    padding: theme.spacing(0.5, 0, 0.5, 0.5),
   },
   labelIcon: {
     marginRight: theme.spacing(1),
@@ -67,11 +65,11 @@ const useTreeItemStyles = makeStyles((theme) => ({
 function StyledTreeItem(props) {
   const classes = useTreeItemStyles();
   const {
-    labelText,
+    bgColor,
+    color,
     labelIcon: LabelIcon,
     labelInfo,
-    color,
-    bgColor,
+    labelText,
     ...other
   } = props;
 
@@ -97,6 +95,7 @@ function StyledTreeItem(props) {
         content: classes.content,
         expanded: classes.expanded,
         selected: classes.selected,
+        focused: classes.focused,
         group: classes.group,
         label: classes.label,
       }}
diff --git a/docs/src/pages/components/tree-view/GmailTreeView.tsx b/docs/src/pages/components/tree-view/GmailTreeView.tsx
index 626e386080b432..0dba1910ecbfca 100644
--- a/docs/src/pages/components/tree-view/GmailTreeView.tsx
+++ b/docs/src/pages/components/tree-view/GmailTreeView.tsx
@@ -33,16 +33,6 @@ const useTreeItemStyles = makeStyles((theme: Theme) =>
   createStyles({
     root: {
       color: theme.palette.text.secondary,
-      '&:hover > $content': {
-        backgroundColor: theme.palette.action.hover,
-      },
-      '&:focus > $content, &$selected > $content': {
-        backgroundColor: `var(--tree-view-bg-color, ${theme.palette.grey[400]})`,
-        color: 'var(--tree-view-color)',
-      },
-      '&:focus > $content $label, &:hover > $content $label, &$selected > $content $label': {
-        backgroundColor: 'transparent',
-      },
     },
     content: {
       color: theme.palette.text.secondary,
@@ -50,9 +40,16 @@ const useTreeItemStyles = makeStyles((theme: Theme) =>
       borderBottomRightRadius: theme.spacing(2),
       paddingRight: theme.spacing(1),
       fontWeight: theme.typography.fontWeightMedium,
-      '$expanded > &': {
+      '&$expanded': {
         fontWeight: theme.typography.fontWeightRegular,
       },
+      '&:hover': {
+        backgroundColor: theme.palette.action.hover,
+      },
+      '&$focused, &$selected, &$selected$focused': {
+        backgroundColor: `var(--tree-view-bg-color, ${theme.palette.action.selected})`,
+        color: 'var(--tree-view-color)',
+      },
     },
     group: {
       marginLeft: 0,
@@ -62,6 +59,7 @@ const useTreeItemStyles = makeStyles((theme: Theme) =>
     },
     expanded: {},
     selected: {},
+    focused: {},
     label: {
       fontWeight: 'inherit',
       color: 'inherit',
@@ -69,7 +67,7 @@ const useTreeItemStyles = makeStyles((theme: Theme) =>
     labelRoot: {
       display: 'flex',
       alignItems: 'center',
-      padding: theme.spacing(0.5, 0),
+      padding: theme.spacing(0.5, 0, 0.5, 0.5),
     },
     labelIcon: {
       marginRight: theme.spacing(1),
@@ -84,11 +82,11 @@ const useTreeItemStyles = makeStyles((theme: Theme) =>
 function StyledTreeItem(props: StyledTreeItemProps) {
   const classes = useTreeItemStyles();
   const {
-    labelText,
+    bgColor,
+    color,
     labelIcon: LabelIcon,
     labelInfo,
-    color,
-    bgColor,
+    labelText,
     ...other
   } = props;
 
@@ -114,6 +112,7 @@ function StyledTreeItem(props: StyledTreeItemProps) {
         content: classes.content,
         expanded: classes.expanded,
         selected: classes.selected,
+        focused: classes.focused,
         group: classes.group,
         label: classes.label,
       }}
diff --git a/packages/material-ui-lab/src/PaginationItem/PaginationItem.js b/packages/material-ui-lab/src/PaginationItem/PaginationItem.js
index 7133b5362392c2..bf91b0720d3aaa 100644
--- a/packages/material-ui-lab/src/PaginationItem/PaginationItem.js
+++ b/packages/material-ui-lab/src/PaginationItem/PaginationItem.js
@@ -39,7 +39,7 @@ export const styles = (theme) => ({
     },
     '&$selected': {
       backgroundColor: theme.palette.action.selected,
-      '&:hover, &$focusVisible': {
+      '&:hover': {
         backgroundColor: fade(
           theme.palette.action.selected,
           theme.palette.action.selectedOpacity + theme.palette.action.hoverOpacity,
@@ -49,6 +49,12 @@ export const styles = (theme) => ({
           backgroundColor: theme.palette.action.selected,
         },
       },
+      '&$focusVisible': {
+        backgroundColor: fade(
+          theme.palette.action.selected,
+          theme.palette.action.selectedOpacity + theme.palette.action.focusOpacity,
+        ),
+      },
       '&$disabled': {
         opacity: 1,
         color: theme.palette.action.disabled,
@@ -135,7 +141,7 @@ export const styles = (theme) => ({
       '&:hover, &$focusVisible': {
         backgroundColor: fade(
           theme.palette.primary.main,
-          theme.palette.action.activatedOpacity + theme.palette.action.hoverOpacity,
+          theme.palette.action.activatedOpacity + theme.palette.action.focusOpacity,
         ),
         // Reset on touch devices, it doesn't add specificity
         '@media (hover: none)': {
@@ -156,7 +162,7 @@ export const styles = (theme) => ({
       '&:hover, &$focusVisible': {
         backgroundColor: fade(
           theme.palette.secondary.main,
-          theme.palette.action.activatedOpacity + theme.palette.action.hoverOpacity,
+          theme.palette.action.activatedOpacity + theme.palette.action.focusOpacity,
         ),
         // Reset on touch devices, it doesn't add specificity
         '@media (hover: none)': {
diff --git a/packages/material-ui-lab/src/TreeItem/TreeItem.d.ts b/packages/material-ui-lab/src/TreeItem/TreeItem.d.ts
index aff614ab7ddbbb..5d57784f47d147 100644
--- a/packages/material-ui-lab/src/TreeItem/TreeItem.d.ts
+++ b/packages/material-ui-lab/src/TreeItem/TreeItem.d.ts
@@ -55,6 +55,7 @@ export type TreeItemClassKey =
   | 'root'
   | 'expanded'
   | 'selected'
+  | 'focused'
   | 'group'
   | 'content'
   | 'iconContainer'
diff --git a/packages/material-ui-lab/src/TreeItem/TreeItem.js b/packages/material-ui-lab/src/TreeItem/TreeItem.js
index 149db4c81ede70..8b8fa806a2b9da 100644
--- a/packages/material-ui-lab/src/TreeItem/TreeItem.js
+++ b/packages/material-ui-lab/src/TreeItem/TreeItem.js
@@ -15,28 +15,7 @@ export const styles = (theme) => ({
     margin: 0,
     padding: 0,
     outline: 0,
-    WebkitTapHighlightColor: 'transparent',
-    '&:focus > $content $label': {
-      backgroundColor: theme.palette.action.hover,
-    },
-    '&$selected > $content $label': {
-      backgroundColor: fade(theme.palette.primary.main, theme.palette.action.selectedOpacity),
-    },
-    '&$selected > $content $label:hover, &$selected:focus > $content $label': {
-      backgroundColor: fade(
-        theme.palette.primary.main,
-        theme.palette.action.selectedOpacity + theme.palette.action.hoverOpacity,
-      ),
-      // Reset on touch devices, it doesn't add specificity
-      '@media (hover: none)': {
-        backgroundColor: 'transparent',
-      },
-    },
   },
-  /* Pseudo-class applied to the root element when expanded. */
-  expanded: {},
-  /* Pseudo-class applied to the root element when selected. */
-  selected: {},
   /* Styles applied to the `role="group"` element. */
   group: {
     margin: 0,
@@ -49,7 +28,43 @@ export const styles = (theme) => ({
     display: 'flex',
     alignItems: 'center',
     cursor: 'pointer',
+    WebkitTapHighlightColor: 'transparent',
+    '&:hover': {
+      backgroundColor: theme.palette.action.hover,
+      // Reset on touch devices, it doesn't add specificity
+      '@media (hover: none)': {
+        backgroundColor: 'transparent',
+      },
+    },
+    '&$focused': {
+      backgroundColor: theme.palette.action.focus,
+    },
+    '&$selected': {
+      backgroundColor: fade(theme.palette.primary.main, theme.palette.action.selectedOpacity),
+      '&:hover': {
+        backgroundColor: fade(
+          theme.palette.primary.main,
+          theme.palette.action.selectedOpacity + theme.palette.action.hoverOpacity,
+        ),
+        // Reset on touch devices, it doesn't add specificity
+        '@media (hover: none)': {
+          backgroundColor: fade(theme.palette.primary.main, theme.palette.action.selectedOpacity),
+        },
+      },
+      '&$focused': {
+        backgroundColor: fade(
+          theme.palette.primary.main,
+          theme.palette.action.selectedOpacity + theme.palette.action.focusOpacity,
+        ),
+      },
+    },
   },
+  /* Pseudo-class applied to the content element when expanded. */
+  expanded: {},
+  /* Pseudo-class applied to the content element when selected. */
+  selected: {},
+  /* Pseudo-class applied to the content element when focused. */
+  focused: {},
   /* Styles applied to the tree node icon and collapse/expand icon. */
   iconContainer: {
     marginRight: 4,
@@ -66,13 +81,6 @@ export const styles = (theme) => ({
     width: '100%',
     paddingLeft: 4,
     position: 'relative',
-    '&:hover': {
-      backgroundColor: theme.palette.action.hover,
-      // Reset on touch devices, it doesn't add specificity
-      '@media (hover: none)': {
-        backgroundColor: 'transparent',
-      },
-    },
   },
 });
 
@@ -189,6 +197,7 @@ const TreeItem = React.forwardRef(function TreeItem(props, ref) {
 
   const handleMouseDown = (event) => {
     if (event.shiftKey || event.ctrlKey || event.metaKey) {
+      // Prevent text selection
       event.preventDefault();
     }
 
@@ -363,16 +372,18 @@ const TreeItem = React.forwardRef(function TreeItem(props, ref) {
   if (multiSelect) {
     ariaSelected = selected;
   } else if (selected) {
-    // single-selection trees unset aria-selected
+    /* single-selection trees unset aria-selected on un-selected items.
+     *
+     * If the tree does not support multiple selection, aria-selected
+     * is set to true for the selected node and it is not present on any other node in the tree.
+     * Source: https://www.w3.org/TR/wai-aria-practices/#TreeView
+     */
     ariaSelected = true;
   }
 
   return (
     <li
-      className={clsx(classes.root, className, {
-        [classes.expanded]: expanded,
-        [classes.selected]: selected,
-      })}
+      className={clsx(classes.root, className)}
       role="treeitem"
       onKeyDown={handleKeyDown}
       onFocus={handleFocus}
@@ -383,7 +394,11 @@ const TreeItem = React.forwardRef(function TreeItem(props, ref) {
       {...other}
     >
       <div
-        className={classes.content}
+        className={clsx(classes.content, {
+          [classes.expanded]: expanded,
+          [classes.selected]: selected,
+          [classes.focused]: focused,
+        })}
         onClick={handleClick}
         onMouseDown={handleMouseDown}
         ref={contentRef}
diff --git a/packages/material-ui-lab/src/TreeItem/TreeItem.test.js b/packages/material-ui-lab/src/TreeItem/TreeItem.test.js
index 9c4a6485cce199..0a67a33529abec 100644
--- a/packages/material-ui-lab/src/TreeItem/TreeItem.test.js
+++ b/packages/material-ui-lab/src/TreeItem/TreeItem.test.js
@@ -928,7 +928,6 @@ describe('<TreeItem />', () => {
           fireEvent.keyDown(getByTestId('one'), { key: ' ' });
 
           expect(getByTestId('one')).to.have.attribute('aria-selected', 'true');
-          expect(getByTestId('one')).to.have.class('Mui-selected');
         });
 
         it('should not select a node when space is pressed and disableSelection', () => {