public function renderTree( $tree = NULL ){														//  
		$list	= array();																			//  
		if( is_null( $tree ) )																		//  
			$tree	= $this->tree;																	//  
		foreach( $tree as $item ){
			$link	= UI_HTML_Tag::create( 'a', $item->label, array( 'href' => "#".$item->id ) );	//  
			$attributes		= array( 'class' => 'level-'.$item->level );							//  
			$subtree		= $this->renderTree( $item->children );									//  
			$list[]	= UI_HTML_Elements::ListItem( $link.$subtree, 0, $attributes );					//  
		}
		return UI_HTML_Tag::create( 'ul', $list, array( 'class' => 'index-tree' ) );				//  
	}