bitter pecan vs hickory tree

bitter pecan and hickory tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
bitter pecan	Yes	No	No	No
hickory tree	Yes	No	No	No

As nouns, hickory tree is a hypernym of bitter pecan; that is, hickory tree is a word with a broader meaning than bitter pecan:

bitter pecan: hickory of southern United States having many narrow leaflets and rather bitter nuts
hickory tree: American hardwood tree bearing edible nuts

Other hypernyms of bitter pecan include hickory.

bitter pecan (noun)	hickory tree (noun)
hickory of southern United States having many narrow leaflets and rather bitter nuts	American hardwood tree bearing edible nuts