sour orange vs orange tree

sour orange and orange tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
sour orange	Yes	No	No	No
orange tree	Yes	No	No	No

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

sour orange: any of various common orange trees yielding sour or bitter fruit; used as grafting stock
orange tree: any citrus tree bearing oranges

Other hypernyms of sour orange include orange.

sour orange (noun)	orange tree (noun)
highly acidic orange used especially in marmalade	any citrus tree bearing oranges
any of various common orange trees yielding sour or bitter fruit; used as grafting stock