branch <- function(len) {

  line(0, 0, 0, -len);
  translate(0, -len);

  len = len * 0.66;

  if (len > 2) {
    pushMatrix();
    rotate(PI/6);

    branch(len);
    popMatrix();

    pushMatrix();
    rotate(-PI/6);
    branch(len);
    popMatrix();
  }
}

settings <- function(){
  size(300, 200)
}

draw <- function() {
  background(255);

  theta = map(mouseX,0,width,0,PI/2);

  translate(width/2, height);
  stroke(0);
  branch(60);
}

settings()
draw()