walnut vs walnut tree

walnut and walnut tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
walnut	Yes	No	No	No
walnut tree	Yes	No	No	No

As nouns, walnut and walnut tree are synonyms defined as:

walnut (noun)	walnut tree (noun)
nut of any of various walnut trees having a wrinkled two-lobed seed with a hard shell	any of various trees of the genus Juglans
any of various trees of the genus Juglans
hard dark-brown wood of any of various walnut trees; used especially for furniture and paneling