pea tree vs shrub

pea tree and shrub both are nouns.

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

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

pea tree: any plant of the genus Caragana having even-pinnate leaves and mostly yellow flowers followed by seeds in a linear pod
shrub: a low woody perennial plant usually having several major stems

Other hypernyms of pea tree include bush.

pea tree (noun)	shrub (noun)
any plant of the genus Caragana having even-pinnate leaves and mostly yellow flowers followed by seeds in a linear pod	a low woody perennial plant usually having several major stems