请教php 数组排序问题

$arr = array(
        'id' => 1, 'pid' => 0, 'title' => '1',
        'id' => 2, 'pid' => 0, 'title' => '2',
        'id' => 3, 'pid' => 0, 'title' => '3',
        'id' => 4, 'pid' => 0, 'title' => '4',
        'id' => 5, 'pid' => 1, 'title' => '1-5',
        'id' => 6, 'pid' => 5, 'title' => '1-5-6',
        'id' => 7, 'pid' => 1, 'title' => '1-7',
        'id' => 8, 'pid' => 2, 'title' => '2-8',
    );

排序完效果

$arr = array(
        'id' => 1, 'pid' => 0, 'title' => '1',
        'id' => 5, 'pid' => 1, 'title' => '1-5',
        'id' => 6, 'pid' => 5, 'title' => '1-5-6',
        'id' => 7, 'pid' => 1, 'title' => '1-7',
        'id' => 2, 'pid' => 0, 'title' => '2',
        'id' => 8, 'pid' => 2, 'title' => '2-8',
        'id' => 3, 'pid' => 0, 'title' => '3',
        'id' => 4, 'pid' => 0, 'title' => '4',
    );

就是父节点后面紧跟子节点