hazelnut vs nut tree

hazelnut and nut tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
hazelnut	Yes	No	No	No
nut tree	Yes	No	No	No

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

hazelnut: any of several shrubs or small trees of the genus Corylus bearing edible nuts enclosed in a leafy husk
nut tree: tree bearing edible nuts

hazelnut (noun)	nut tree (noun)
nut of any of several trees of the genus Corylus	tree bearing edible nuts
any of several shrubs or small trees of the genus Corylus bearing edible nuts enclosed in a leafy husk