red ash vs ash tree

red ash and ash tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
red ash	Yes	No	No	No
ash tree	Yes	No	No	No

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

red ash: smallish American tree with velvety branchlets and lower leaf surfaces
ash tree: any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus

Other hypernyms of red ash include ash.

red ash (noun)	ash tree (noun)
smallish American tree with velvety branchlets and lower leaf surfaces	any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus