【正确答案】import turtle as t
   def tree(length,level):    #树的层次
   if level＜=0:
   return
   t.forward(length)    #前进方向画length距离
   t.left(45)
   tree(0.6*length,level-1)
   t.right(90)
   tree(0.6*length,level-1)
   t.left(45)
   t.backward(length)
   return
   t.pensize(3)
   t.color('green')
   t.left(90)
   tree(100,6)