/**
* @param Hierarchical $sibling
* @return $this
*/
function addSibling($sibling)
{
if (isset($this->parent)) {
$sibling->parent = $this->parent;
$this->parent->addChild($sibling);
}
return $this;
}
public function __construct()
{
parent::__construct();
// $this->_parent = null;
// $this->_value = new Collection();
}