The tree, drawn sideways (root at the left margin):
        80
    70
        60
50
        40
    30
        20

inorder   : 20, 30, 40, 50, 60, 70, 80
preorder  : 50, 30, 20, 40, 70, 60, 80
postorder : 20, 40, 30, 60, 80, 70, 50

inorder output is sorted: yes
