service tree vs shrub

service tree and shrub both are nouns.

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

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

service tree: any of various North American trees or shrubs having showy white flowers and edible blue-black or purplish fruit
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of service tree include bush.

service tree (noun)	shrub (noun)
medium-sized European tree resembling the rowan but bearing edible fruit	a low woody perennial plant usually having several major stems
any of various North American trees or shrubs having showy white flowers and edible blue-black or purplish fruit