import turtle
import random
def tree(n):
    if n>=0:
        if n<=12:
            color_a=["snow","lightcoral"]
            color=random.choice(color_a)
            pen.color(color)
            pen.pensize(n/3)
        else:
            pen.color("sienna")
            pen.pensize(n/10)
        pen.forward(n)
        a=random.randint(0,30)
        l=random.randint(1,15)
        pen.right(a)
        tree(n-15)
        pen.left(2*a)
        tree(n-15)
        pen.right(a)
        pen.up()
        pen.backward(n)
        
        pen.down()
    
pen = turtle.Turtle()
pen.color('sienna')
pen.speed(0)
# 画布大小
w = turtle.Screen()
w.bgcolor('wheat')      # wheat小麦
pen.left(90)
tree(100)