bitter orange vs bitter orange tree

bitter orange and bitter orange tree both are nouns.

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

As nouns, bitter orange and bitter orange tree are synonyms defined as:

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

Other synonyms of bitter orange include bigarade, Citrus aurantium, marmalade orange, Seville orange, sour orange.

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