docs: public void subDivide() {
          northWest = new QuadTree(this, data, new Cell(boundary.getX() - .5 * boundary.getHw(),
                          boundary.getY() - .5 * boundary.getHh(), .5 * boundary.getHw(), .5 * boundary.getHh()));
          northEast = new QuadTree(this, data, new Cell(boundary.getX() + .5 * boundary.getHw(),
                          boundary.getY() - .5 * boundary.getHh(), .5 * boundary.getHw(), .5 * boundary.getHh()));
          southWest = new QuadTree(this, data, new Cell(boundary.getX() - .5 * boundary.getHw(),
                          boundary.getY() + .5 * boundary.getHh(), .5 * boundary.getHw(), .5 * boundary.getHh()));
          southEast = new QuadTree(this, data, new Cell(boundary.getX() + .5 * boundary.getHw(),
                          boundary.getY() + .5 * boundary.getHh(), .5 * boundary.getHw(), .5 * boundary.getHh()));
  
      }