$categories = array(  
    array('id'=>1,'name'=>'電腦','pid'=>0),  
    array('id'=>2,'name'=>'手機','pid'=>0),  
    array('id'=>3,'name'=>'筆記本','pid'=>1),  
    array('id'=>4,'name'=>'桌上型電腦','pid'=>1),  
    array('id'=>5,'name'=>'智慧機','pid'=>2),  
    array('id'=>6,'name'=>'功能機','pid'=>2),  
    array('id'=>7,'name'=>'超級本','pid'=>3),  
    array('id'=>8,'name'=>'遊戲本','pid'=>3),  
    array('id'=>9,'name'=>'安卓','pid'=>5),  
    array('id'=>10,'name'=>'ios','pid'=>5),  
);  
  
function my_category($categories, $pid=0){
	$tree = array();
	foreach($categories as $key=>$value){
		if($value['pid'] == $pid){
			$value['children'] = my_category($categories, $value['id']);
			if($value['children'] == null){
				unset($value['children']);
			}
			$tree[] = $value;
		}
	}
	return $tree;
}

$tree = my_category($categories, 0);
echo '<pre>';print_r($tree);exit;