import random
import turtle

def tree(size, myTurtle):
    myTurtle.pensize(size / 20)

    if size < random.randint(1,2) * 20:
        myTurtle.color("green")
    else:
        myTurtle.color("brown")

    if size > 5:
        myTurtle.forward(size)
        myTurtle.left(25)
        tree(size - random.randint(10, 20), myTurtle)
        myTurtle.right(50)
        tree(size - random.randint(10, 20), myTurtle)
        myTurtle.left(25)
        myTurtle.penup()
        myTurtle.backward(size)
        myTurtle.pendown()

window = turtle.Screen()
window.setup(800,600)
window.bgcolor("white")

myTurtle = turtle.Turtle()
myTurtle.color("brown", "blue")
myTurtle.left(90)
myTurtle.speed(0)
myTurtle.penup()
myTurtle.setpos(0, -250)
myTurtle.pendown()