bitter orange tree vs genus Citrus

bitter orange tree and genus Citrus both are nouns.

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

bitter orange tree (noun)	genus Citrus (noun)
any of various common orange trees yielding sour or bitter fruit; used as grafting stock	orange, lemon, lime, etc.