my_tree.py

import turtle
import random
pen = turtle.Turtle()
pen.color('sienna')
# 画布大小
w = turtle.Screen()
w.bgcolor('wheat')      # wheat小麦

# 移动到起点
pen.left(90)
pen.up()
pen.backward(150)    # 后退
pen.down()

def tree(n):
    if n>=0:
        if n<=12:
            color=random.choice(["snow","lightcoale"])
            pen.color((color))
            pen.pensize(n/3)
        else:
            pen.color("sienna")
            pen.pensize(n/10)
        pen.forward(n)
        angle=random.randint(0,30)
        length=random.randint(0,20)
        pen.right(angle)
        tree(n-length)
        pen.left(2*angle)
        tree(n-length)
        pen.right(angle)
        pen.up()
        pen.backward(n)
        pen.down()
tree(50)
turtle.done()