gallows vs gallows tree

gallows and gallows tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
gallows	Yes	No	No	No
gallows tree	Yes	No	No	No

As nouns, gallows tree is a hyponym of gallows; that is, gallows tree is a word with a more specific, narrower meaning than gallows:

gallows: an instrument of execution consisting of a wooden frame from which a condemned person is executed by hanging
gallows tree: alternative terms for gallows

Other hyponyms of gallows include gallous, gallows-tree, gibbet.

gallows (noun)	gallows tree (noun)
an instrument of execution consisting of a wooden frame from which a condemned person is executed by hanging	alternative terms for gallows