red dogwood vs dogwood tree

red dogwood and dogwood tree both are nouns.

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

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

red dogwood: common North American shrub with reddish purple twigs and white flowers
dogwood tree: a tree of shrub of the genus Cornus often having showy bracts resembling flowers

Other hypernyms of red dogwood include cornel, dogwood.

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

red dogwood: European deciduous shrub turning red in autumn having dull white flowers
dogwood tree: a tree of shrub of the genus Cornus often having showy bracts resembling flowers

Other hypernyms of red dogwood include cornel, dogwood.

red dogwood (noun)	dogwood tree (noun)
common North American shrub with reddish purple twigs and white flowers	a tree of shrub of the genus Cornus often having showy bracts resembling flowers
European deciduous shrub turning red in autumn having dull white flowers