def isBST(root):
    if root.left and root.left.data >= root.data:
        return False
    if root.left:
        print(root.left.data,"<",root.data)
    if root.right and root.right.data <= root.data:
        return False
    if root.right:
        print(root.right.data,">",root.data)
    return True

def checkBST(root):
    if not isBST(root):
        return False
    if root.left:
        checkBST(root.left)
    if root.right:
        checkBST(root.right)
    return True

2
1 2 4 3 5 6 7

2 < 3
6 > 3
1 < 2
4 > 2
5 < 6
7 > 6
Yes