butternut vs walnut tree

butternut and walnut tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
butternut	Yes	No	No	No
walnut tree	Yes	No	No	No

As nouns, walnut tree is a hypernym of butternut; that is, walnut tree is a word with a broader meaning than butternut:

butternut: North American walnut tree having light-brown wood and edible nuts; source of a light-brown dye
walnut tree: any of various trees of the genus Juglans

Other hypernyms of butternut include walnut.

butternut (noun)	walnut tree (noun)
oily egg-shaped nut of an American tree of the walnut family	any of various trees of the genus Juglans
North American walnut tree having light-brown wood and edible nuts; source of a light-brown dye