import turtle
import random
pen = turtle.Pen()
pen.color("sienna")
pen.speed(1)
# 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_list=["snow","lightcoral"]
            color=random.choice(color_list)
            pen.color(color)
            pen.pensize(n/3)
        else:
            pen.color("sienna")
            pen.pensize(n/10)
        pen.forward(n)
        angle=random.random()
        pen.right(30*angle)
        length=1.5*random.random()
        tree(n-10*length)
        pen.left(60*angle)
        tree(n-10*length)
        pen.right(30*angle)
        pen.up()
        pen.backward(n)
        pen.down()
tree(60)
turtle.done()