Python : Tree implementation

class Node:
    def __init__(self,value):
        self.left = None
        self.data = value
        self.right = None
       
class Tree:
   
    def createNode(self,data):
        return Node(data)
       
    def insert(self,node,data):
        if node is None:
            return self.createNode(data)
        if data < node.data:
            node.left = self.insert(node.left,data)
        elif data > node.data:
            node.right = self.insert(node.right,data)
       
        return node
   
    def traversePreorder(self,root):
        if root is not None:
            print root.data
            self.traversePreorder(root.left)
            self.traversePreorder(root.right)
           
       
def main():
    root = None
    tree = Tree()
    root = tree.insert(root,10)
    print root
    tree.insert(root,20)
    tree.insert(root,30)
    tree.insert(root,40)
    tree.insert(root,70)
   
   
    print "Traverse Inorder"
    tree.traversePreorder(root)
   
if __name__ == "__main__":
    main()