public static void main(String[] args) {
   BinaryTreeNode<Integer> root = new BinaryTreeNode<Integer>(3);
   BinaryTreeNode<Integer> node1 = new BinaryTreeNode<Integer>(1);
   BinaryTreeNode<Integer> node2 = new BinaryTreeNode<Integer>(5);
   BinaryTreeNode<Integer> node3 = new BinaryTreeNode<Integer>(0);
   BinaryTreeNode<Integer> node4 = new BinaryTreeNode<Integer>(2);
   BinaryTreeNode<Integer> node5 = new BinaryTreeNode<Integer>(-1);
   BinaryTreeNode<Integer> node6 = new BinaryTreeNode<Integer>(4);
   root.setLeft(node1);
   root.setRight(node2);
   node1.setLeft(node3);
   node1.setRight(node4);
   node3.setLeft(node5);
   node2.setLeft(node6);
   BinaryTreeBST bst = new BinaryTreeBST();
   System.out.println(bst.isBST(root));
 }