citrus tree vs fruit tree

citrus tree and fruit tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
citrus tree	Yes	No	No	No
fruit tree	Yes	No	No	No

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

citrus tree: any of numerous tropical usually thorny evergreen trees of the genus Citrus having leathery evergreen leaves and widely cultivated for their juicy edible fruits having leathery aromatic rinds
fruit tree: tree bearing edible fruit

citrus tree (noun)	fruit tree (noun)
any of numerous tropical usually thorny evergreen trees of the genus Citrus having leathery evergreen leaves and widely cultivated for their juicy edible fruits having leathery aromatic rinds	tree bearing edible fruit