Salix babylonica vs willow tree

Salix babylonica and willow tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
Salix babylonica	Yes	No	No	No
willow tree	Yes	No	No	No

As nouns, willow tree is a hypernym of Salix babylonica; that is, willow tree is a word with a broader meaning than Salix babylonica:

Salix babylonica: willow with long drooping branches and slender leaves native to China; widely cultivated as an ornamental
willow tree: any of numerous deciduous trees and shrubs of the genus Salix

Other hypernyms of Salix babylonica include willow.

Salix babylonica (noun)	willow tree (noun)
willow with long drooping branches and slender leaves native to China; widely cultivated as an ornamental	any of numerous deciduous trees and shrubs of the genus Salix