php 数组变成树状型结构

<? php
$stime = microtime(true);
$nodes = [
    ['id' = > 1, 'pid' = > 0, 'name' = > 'a'],
    ['id' = > 2, 'pid' = > 0, 'name' = > 'b'],
    ['id' = > 3, 'pid' = > 1, 'name' = > 'c'],
    ['id' = > 4, 'pid' = > 2, 'name' = > 'd'],
    ['id' = > 5, 'pid' = > 6, 'name' = > 'e'],
    ['id' = > 6, 'pid' = > 4, 'name' = > 'f'],
    ['id' = > 7, 'pid' = > 6, 'name' = > 'g'],
    ['id' = > 8, 'pid' = > 6, 'name' = > 'h'],
    ['id' = > 9, 'pid' = > 10, 'name' = > 'i'],
    ['id' = > 10, 'pid' = > 8, 'name' = > 'j']
];

function tree($list, $id = 'id', $pid = 'pid', $name = 'name') {
    $data = [];
    foreach($list as $row) {
        $data[$row[$id]][$name] = $row[$name];
        $data[$row[$pid]]['children'][$row[$id]] = & $data[$row[$id]];
    }
    return isset($data[0]['children']) ? $data[0]['children'] : [];
}
print_r(tree($nodes));
$etime = microtime(true);
echo '运行后内存：'.round(memory_get_usage() / 1024 / 1024, 2).
'MB \r\n';
$total = $etime - $stime; //计算差值
echo "[页面执行时间：{$total} ]秒"; ?>