Introduction - If you have any usage issues, please Google them yourself
A two - fork sort tree or an empty tree, or a two - fork tree with the following properties:
(1) if the left subtree is not empty, the value of all the nodes on the left subtree is less than or equal to the value of its root node.
(2) if the right subtree is not empty, the value of all the nodes on the right subtree is greater than or equal to the value of its root node.
(3) the left and right subtrees are also two forked trees, respectively.