myrobalan plum vs plum tree

myrobalan plum and plum tree both are nouns.

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

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

myrobalan plum: small Asiatic tree bearing edible red or yellow fruit
plum tree: any of several trees producing edible oval fruit having a smooth skin and a single hard stone

Other hypernyms of myrobalan plum include plum.

myrobalan plum (noun)	plum tree (noun)
small Asiatic tree bearing edible red or yellow fruit	any of several trees producing edible oval fruit having a smooth skin and a single hard stone