(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.