PD4CS

#import Python turtle module
#More info see https://docs.python.org/2/library/turtle.html
import turtle

##Make turtle t recursively draw a tree
def drawTree(branchLen,t):
    if branchLen <= 10: #base case
        t.forward(10)
        t.backward(10)
    else:
        #draw the trunk
        t.forward(branchLen)

        #draw branches
        t.right(20)
        drawTree(branchLen-15,t)
        t.left(40)
        drawTree(branchLen-15,t)
        t.right(20)

        #go back to the starting point
        t.backward(branchLen)

##Initialize the turtle
t = turtle.Turtle()
t.speed(6)      #Set the turtle speed. 1 is slow and 10 is fast.
t.color("green")#Set the turtle color.
t.pensize(2)    #Set the pen size
myWin = turtle.Screen()

##Initialize the pen position
t.left(90)      #Turn turtle left by 90 degrees.
t.up()          #Pull the pen up - no drawing when moving.
t.backward(100) #move the pen backward by 100
t.down()        #Pull the pen down - drawing when moving.

#draw the tree
drawTree(70,t)

##exit the drawing screen
myWin.exitonclick()

Program Revised from http://interactivepython.org/runestone/static/pythonds/Recursion/pythondsintro-VisualizingRecursion.html