save project

my_tree.py

@@ -18,6 +18,9 @@ pen.forward(50)
 pen.up()
 pen.forward(-50)
 left(60)
-pen.backward(150) 
+pen.left(90)
+pen.up()
+pen.backward(150)    # 后退
+pen.down()
 pen.forward(50)
 turtle.done()