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class TreeNode:
    def __init__(self,key):
        self.key = key
        self.right = None
        self.left = None
node0 = TreeNode(3)
node1 = TreeNode(4)
node2 = TreeNode(5)
node0
<__main__.TreeNode at 0x7f30c116ec70>
node0.key
3
node0.left = node1
node0.right = node2