text: from tree.tree import TreeNode
  
  
  def bin_tree_to_list(root):
      """
      type root: root class
      """
      if not root:
          return root
      root = bin_tree_to_list_util(root)
      while root.left:
          root = root.left
      return root
  
  
  def bin_tree_to_list_util(root):
      if not root:
          return root
      if root.left:
          left = bin_tree_to_list_util(root.left)
          while left.right:
              left = left.right
          left.right = root
          root.left = left
      if root.right:
          right = bin_tree_to_list_util(root.right)
          while right.left:
              right = right.left
          right.left = root
          root.right = right
      return root
  
  
  def print_tree(root):
      while root:
          print(root.val)
          root = root.right
  