Anki provides some special fields that can be referenced in your notes. In addition to the built-in Deck and Subdeck, this addon provides access to a RootDeck field. It works like this:
Deck: Foods::Fruits::Watermelon
Subdeck: Watermelon
RootDeck: Foods
Whereas the Deck field is always the full string you enter, RootDeck will always just be the first. I use it purely for some fancy aesthetics:
the above is for the deck Code::DistributedSystems.
Copy add-root-deck-field.py to your Anki addon folder (Tools > Add-ons > Open Add-ons folder...). Restart Anki.
Once installed, {{RootDeck}} will be available inside any template.