wild apple vs apple tree

wild apple and apple tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
wild apple	Yes	No	No	No
apple tree	Yes	No	No	No

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

wild apple: any of numerous wild apple trees usually with small acidic fruit
apple tree: any tree of the genus Malus especially those bearing firm rounded edible fruits

wild apple (noun)	apple tree (noun)
any of numerous wild apple trees usually with small acidic fruit	any tree of the genus Malus especially those bearing firm rounded edible fruits