bitter orange tree vs Citrus aurantium

bitter orange tree and Citrus aurantium both are nouns.

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

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

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

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

bitter orange tree (noun)	Citrus aurantium (noun)
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