float ugao = QUARTER_PI;
float pomeraj = 0;

void setup() {
  size(600, 400);
  background(0);
  stroke(255);
}

void draw() {
  background(0);
  translate(width/2, height);
  pomeraj = mouseX * QUARTER_PI/width  - PI/8;
  stablo(120, 8);
}

void stablo(float dim, int n) {
  line(0, 0, 0, -dim);
  translate(0, -dim);
  if (n > 1) {
    pushMatrix(); 
    rotate(ugao + pomeraj);
    stablo(2*dim/3, n-1);
    popMatrix();
    pushMatrix();
    rotate(-ugao + pomeraj);
    stablo(2*dim/3, n-1);
    popMatrix();
  }
}