staff tree vs shrub

staff tree and shrub both are nouns.

Word	Noun	Adjective	Verb	Adverb
staff tree	Yes	No	No	No
shrub	Yes	No	No	No

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

Other hypernyms of staff tree include bush.

staff tree (noun)	shrub (noun)
any small tree or twining shrub of the genus Celastrus	a low woody perennial plant usually having several major stems