big-bud hickory vs hickory tree

big-bud hickory and hickory tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
big-bud hickory	Yes	No	No	No
hickory tree	Yes	No	No	No

As nouns, hickory tree is a hypernym of big-bud hickory; that is, hickory tree is a word with a broader meaning than big-bud hickory:

big-bud hickory: smooth-barked North American hickory with 7 to 9 leaflets bearing a hard-shelled edible nut
hickory tree: American hardwood tree bearing edible nuts

Other hypernyms of big-bud hickory include hickory.

big-bud hickory (noun)	hickory tree (noun)
smooth-barked North American hickory with 7 to 9 leaflets bearing a hard-shelled edible nut	American hardwood tree bearing edible nuts