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_list=['snow','lightcoral']
            color=random.choice(color_list)
            pen.color(color)
            pen.pensize(n/3)
        else:
            pen.color('sienna')
            pen.pensize(n/10)
        a=random.randint(0,30)
        b=random.randint(1,15)
        pen.forward(n)
        pen.right(a)
        tree(n-b)
        
        
        pen.left(a*2)
        tree(n-b)
        pen.right(a)
        pen.up()
        pen.backward(n)
        
        pen.down()



tree(60)



turtle.done()