levelorder dataorder example
1 2 3 4 5 6 7 8 9
0 0 0 1 1 2 3 5 5
   inorder dataorder example
7 4 2 5 1 8 6 9 3
1 2 4 2 4 6 8 6 4
   preorder dataorder example
1 2 4 7 5 3 6 8 9
0 0 1 2 1 0 5 6 6
   postorder dataorder example
7 4 5 2 8 9 6 3 1
1 3 3 8 6 6 7 8 8