swamp hickory vs hickory tree

swamp hickory and hickory tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
swamp hickory	Yes	No	No	No
hickory tree	Yes	No	No	No

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

swamp hickory: hickory of the eastern United States having a leaves with 7 or 9 leaflets and thin-shelled very bitter nuts
hickory tree: American hardwood tree bearing edible nuts

Other hypernyms of swamp hickory include hickory.

swamp hickory (noun)	hickory tree (noun)
hickory of the eastern United States having a leaves with 7 or 9 leaflets and thin-shelled very bitter nuts	American hardwood tree bearing edible nuts