while printing the postorder of the tree, i kept getting None as the last value I have no idea which part i did wrong
def postorder(tree): if tree : postorder(tree.get_left_subtree()) postorder(tree.get_right_subtree()) print(tree.get_value(),end = "") def buildTree(inorder, preorder): if len(inorder) == 0: return None if len(inorder) == 1: return ListBinaryTree(inorder[0]) root = ListBinaryTree(preorder[0]) index = inorder.index(preorder[0]) root.left = root.insert_tree_left(buildTree(inorder[0:index], preorder[1: index + 1])) root.right = root.insert_tree_right(buildTree(inorder[index+1 : len(inorder)], preorder[index + 1 : len(preorder)-1])) return root 
