Create a fractal tree

Context Free, 82 65 57 characters

rule T{9*[y 1]SQUARE[]2*{f 90}T{s.75y 8r 25}}startshape T

See: http://www.contextfreeart.org/gallery/view.php?id=3384

Golf'd further with help from Context Free Art users minimaleye, MtnViewJohn, and kipling.

Python - 215

import turtle
t=turtle.Turtle()
def f(w):
    if w>=1:
        s=t.pensize()
        t.pensize(w)
        t.fd(w*9)
        t.rt(20)
        f(w*.75)
        t.lt(40)
        f(w*.75)
        t.right(20)
        t.bk(w*9)
        t.pensize(w)
t.speed(9)
f(9)
t.ht()
raw_input()

Close enough?

Logo, 88, 86

to t:d if:d=0[stop]setpensize:d*.75 fd:d*7 rt 25 t:d-1 lt 50 t:d-1 rt 25 bk:d*7end t [numsteps]

Edit: Made the branches decrease as pointed out in the comments.