arborvitae vs coniferous tree

arborvitae and coniferous tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
arborvitae	Yes	No	No	No
coniferous tree	Yes	No	No	No

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

arborvitae: any of several Asian and North American conifers of the genera Thuja and Thujopsis
coniferous tree: any gymnospermous tree or shrub bearing cones

Other hypernyms of arborvitae include conifer.

arborvitae (noun)	coniferous tree (noun)
any of several Asian and North American conifers of the genera Thuja and Thujopsis	any gymnospermous tree or shrub bearing cones