litchi vs fruit tree

litchi and fruit tree both are nouns.

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

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

litchi: Chinese tree cultivated especially in Philippines and India for its edible fruit; sometimes placed in genus Nephelium
fruit tree: tree bearing edible fruit

litchi (noun)	fruit tree (noun)
Chinese fruit having a thin brittle shell enclosing a sweet jellylike pulp and a single seed; often dried	tree bearing edible fruit
Chinese tree cultivated especially in Philippines and India for its edible fruit; sometimes placed in genus Nephelium