This also breaks the show() function of this trivial binary tree.

Patch coming in a couple minutes.

Warning: compatibility with queue not checked, I'm still working off 5.9 sage-main with only #8703 installed.

Apply: nothing. This is a duplicate ticket.

CC: @fchapoton @sagetrac-sage-combinat @VivianePons @hivert

Component: combinatorics

Keywords: binary trees, trees

Author: Darij Grinberg

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/14564