tree surgeon vs specialist

tree surgeon and specialist both are nouns.

Word	Noun	Adjective	Verb	Adverb
tree surgeon	Yes	No	No	No
specialist	Yes	No	No	No

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

tree surgeon: a specialist in treating damaged trees
specialist: an expert who is devoted to one occupation or branch of learning

Other hypernyms of tree surgeon include specialiser, specializer.

tree surgeon (noun)	specialist (noun)
a specialist in treating damaged trees	an expert who is devoted to one occupation or branch of learning
	practices one branch of medicine