php generates infinite column tree

$arr=Array(
    Array('cid' => 2,'cname' => '新闻','pid' => 0),
    Array('cid' => 4,'cname' =>'体育','pid' => 0),
    Array('cid' => 5,'cname' => '娱乐','pid' => 0),
    Array('cid' => 7,'cname' => '热点新闻','pid' =>2),
    Array('cid' => 8,'cname' => '小众新闻','pid' => 2),
    Array('cid' => 9,'cname' => '民谣新闻','pid' => 8),
);