apple vs apple tree

apple and apple tree both are nouns.

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

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

apple: native Eurasian tree widely cultivated in many varieties for its firm rounded edible fruits
apple tree: any tree of the genus Malus especially those bearing firm rounded edible fruits

apple (noun)	apple tree (noun)
fruit with red or yellow or green skin and sweet to tart crisp whitish flesh	any tree of the genus Malus especially those bearing firm rounded edible fruits
native Eurasian tree widely cultivated in many varieties for its firm rounded edible fruits