wild plum tree vs wild plum

wild plum tree and wild plum both are nouns.

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

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

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