Next node binary tree Python

Given a binary tree and a node which, find the next node in a preorder traversal order and returns. It includes not only the book node about the child nodes while the parent node contain pointers.

class TreeLinkNode:
    def __init__(self,x):
        self.val = x
        self.left = None
        self.right =None
        self.next =None

class Solution:
    def GetNext(self,pNode):
        # 1. 寻找右子树，如果存在就一直找到右子树的最左边，就是下一个节点
        # 2. 没有右子树，就寻找它的父节点，一直找到它是父节点的左子树，打印父节点
        if pNode.right:
            tmpNode = pNode.right
            while tmpNode.left:
                tmpNode=tmpNode.left
            return tmpNode
        else:
            tmpNode = pNode
            while tmpNode.next:
                if tmpNode.next.left == tmpNode:
                    return tmpNode.next
                tmpNode = tmpNode.next
            return  None