protected function getPrefix()
  {
    $prefix = "";

    if(count($this->currSib))
    {
      $last = array_pop($this->currSib);

      foreach($this->currSib as $sibling)
      {
        $prefix .=  ($sibling) ? "| " : "  ";
      }

      $prefix .= ($last) ? "\\-" : "|-";
    }

    return $prefix;
  }