Run Tree Structure in Python

I implemented tree structure as follow:

class TreeNode(object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution(object):
    def maxDepth(self, root):
        ...

    def isBST(self, curr):
        ...

def main():
    one = TreeNode(1)
    two = TreeNode(2)
    three = TreeNode(3)
    two.left = one
    two.right = three
    Solution.isBST(self, two)

if __name__ == "__main__":
    main()

I’m not sure how to run it, it’s giving me an error on Solution.isBST(self, two), I guess it’s because self is not defined.

However, if I do :

Solution.isBST(two)

It says the function is missing an argument. So I guess self must be called?.
If I do

self.isBST(two)

Then, I’m not sure where to reference self in the first place. Anyone knows how to run it?