wild plum vs wild plum tree

wild plum and wild plum tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
wild plum	Yes	No	No	No
wild plum tree	Yes	No	No	No

As nouns, wild plum and wild plum tree are synonyms defined as:

wild plum (noun)	wild plum tree (noun)
fruit of the wild plum of southern United States	an uncultivated plum tree or shrub
an uncultivated plum tree or shrub