a.py

import turtle
pen=turtle.Turtle()
pen.color('sienna')
w=turtle.Screen()
w.bgcolor('wheat')
pen.left(90)
pen.up()
pen.backward(150)
pen.down()
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()
tree(100)
turtle.done()