big shagbark vs hickory tree

big shagbark and hickory tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
big shagbark	Yes	No	No	No
hickory tree	Yes	No	No	No

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

big shagbark: hickory of the eastern United States resembling the shagbark but having a much larger nut
hickory tree: American hardwood tree bearing edible nuts

Other hypernyms of big shagbark include hickory.

big shagbark (noun)	hickory tree (noun)
hickory of the eastern United States resembling the shagbark but having a much larger nut	American hardwood tree bearing edible nuts