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