anchor.diff:    }
   
     render() {
  -    //game.debug.quadTree(game.physics.arcade.quadTree);
  +    game.debug.quadTree(game.physics.arcade.quadTree);
     }
   }
  
positive.code: 
    create() {
  
      game.world.setBounds(0, 0, 250, 250);
  
      game.physics.startSystem(Physics.ARCADE);
  
  
negative.code:     aliens = game.add.group();
      aliens.enableBody = true;
  
      for (var i = 0; i < 200; i++) {
        Sprite s = aliens.create(game.world.randomX, game.world.randomY, 'baddie');
        s.scale.set(1);
        s.body.collideWorldBounds = true;
  