Green’s Dictionary of Slang

Gregorian tree n.

the gallows.

1641		Mercurius Pragmaticus cited in Grose 1785 n.p.: This trembles under the black rod, and he / Doth fear his fate from the Gregorian tree.
1785		Grose Classical Dict. of the Vulgar Tongue n.p.: The predecessor of Dun, was Gregory Brandon, from whom the gallows was called, the Gregorian tree.
1796		Grose Classical Dict. of the Vulgar Tongue (3rd edn) n.p.: Gregorian Tree. The gallows: so named from Gregory Brandon, a famous finisher of the law; to whom Sir William Segar, garter king of arms (being imposed on by Brooke, a herald), granted a coat of arms.
1811		Lex. Balatronicum [as cit. 1796].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.