define segment(i) {
  if (i - 4000) {
    pen(i/20000+1)
    color(0,255-i*255/15000,0)
    forward(i/1000)
    split { right(30) segment(i*8/10) }
            left(30)  segment(i*8/10)
  }
}

forward(-100)
pen(1)
segment(80000)