What is "boottree"

Boottree \Boot"tree`\, n. [Boot + tree wood, timber.] An instrument to stretch and widen the leg of a boot, consisting of two pieces, together shaped like a leg, between which, when put into the boot, a wedge is driven.

The pretty boots trimly stretched on boottrees.
--Thackeray.

n. a device, shaped like a divided leg with a wedge, used to stretch the leg of a boot