Seville orange vs orange tree

Seville orange and orange tree both are nouns.

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

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

Seville 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 Seville orange include orange.

Seville 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