Suppose there is a binary search tree. We perform the postorder traversal on the binary search tree and print out the corresponding keys when the nodes are visited. The order of the keys is

3, 7, 6, 10, 13, 12, 5, 18, 23, 20, 16, 15

Please show the image of the binary search tree.

Remark: If there are more than one binary search trees which output 3, 7, 6, 10, 13, 12, 5, 18, 23, 20, 16, 15 when performing postorder traversal, just show one such binary search tree.