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()
# pen.forward(100)
# pen.right(30)
# pen.forward(50)
# pen.penup()
# pen.backward(50)
# pen.left(60)
# pen.pendown()
# pen.forward(50)
# pen.penup()
# pen.backward(50)
# pen.right(30)
# pen.backward(100)
# def tree(n):
#     if n>=50:
#         pen.forward(n)
#         pen.right(30)
#         tree(n-50)
#         pen.left(60)
#         tree(n-50)
#         pen.right(30)
#         pen.up()
#         pen.backward(n)
#         pen.down()
def tree(n):
    if n>=0:
        if n<=12:
            color_list = ['snow','lightcoral']
            color = random.choice(color_list)
            pen.pencolor(color)
            pen.pensize(n/3)
        else:
            pen.pencolor('sienna')
            pen.pensize(n/10)
        pen.forward(n)
        angle = random.randint(0,30)
        length = random.randint(1,15)
        pen.right(angle)
        tree(n-length)
        pen.left(2*angle)
        tree(n-length)
        pen.right(angle)
        pen.up()
        pen.backward(n)
        pen.down()
tree(60)
turtle.done()