(trace cons)
(preorder bushy-tree)
|(cons 1 ())
|(1)
|(cons 3 ())
|(3)
|(cons 1 (3))
|(1 3)
|(cons 2 (1 3))
|(2 1 3)
|(cons 5 ())
|(5)
|(cons 7 ())
|(7)
|(cons 5 (7))
|(5 7)
|(cons 6 (5 7))
|(6 5 7)
|(cons 3 (6 5 7))
|(3 6 5 7)
|(cons 1 (3 6 5 7))
|(1 3 6 5 7)
|(cons 2 (1 3 6 5 7))
|(2 1 3 6 5 7)
|(cons 4 (2 1 3 6 5 7))
|(4 2 1 3 6 5 7)
(4 2 1 3 6 5 7)
12 calls to cons, including consing some leaves multiple times.