comefrom: <doocs>1305.All Elements in Two Binary Search Trees_2.py
code: def dfs(root, t):
      if root is None:
          return
      dfs(root.left, t)
      t.append(root.val)
      dfs(root.right, t)
masked: def sample_funcname ( var_1 , var_2 ) :
      if var_1 is None :
          return
      var_0 ( var_1.left , var_2 )
      var_2.append ( var_1.val )
      var_0 ( var_1.right , var_2 )
  