
In this tree, the root contains key 35, every key in the left subtree
of the root is less than 35 (these are 11, 20, and 29), and every key in
the right subtree is greater than 35 (these are 40, 43, 47, 50, 60,
65, and 72).
This property is true of every node in the tree. For example, the node containing key 50 has 40, 43, and 47 in its left subtree, and has 60, 65, and 72 in its right subtree. 
(Other applets by James Stewart)