多維數(shù)組分類樹 組合html樹的問題？（遞歸）

數(shù)組結(jié)構(gòu)是這樣的：

然后組裝成html結(jié)構(gòu)的方法如下：

function creatHtmlTree($tree)
{
    static $htmlTree;
    $htmlTree .= '<ul>';
    foreach ($tree as $key => $value) {
        $htmlTree .= "<li><span><i class='icon-folder-open'></i>{$value['name']} </span> <a href=''>Goes somewhere</a>";
        if (isset($value['childs']) && is_array($value['childs'])) {
            $html = creatHtmlTree($value['childs']);
            $htmlTree .= $html;
        } 
        $htmlTree .= "</li>";
    }
    $htmlTree .= "</ul>";
    return $htmlTree;
}

但是實(shí)際上輸出的結(jié)果是錯(cuò)誤的：

自己猜想，一定是自己的遞歸邏輯有問題，但是實(shí)在是想不明白問題到底出在哪里。所以還請(qǐng)幫忙看下，那段遞歸代碼有什么問題

另外貼出完整的測(cè)試代碼：

<?php

$data[] =array('id'=>1,'parentid'=>0,'name'=>'中國');
$data[] =array('id'=>2,'parentid'=>0,'name'=>'美國');
$data[] =array('id'=>3,'parentid'=>0,'name'=>'韓國');
$data[] =array('id'=>4,'parentid'=>1,'name'=>'北京');
$data[] =array('id'=>5,'parentid'=>1,'name'=>'上海');
$data[] =array('id'=>6,'parentid'=>1,'name'=>'廣西');
$data[] =array('id'=>7,'parentid'=>6,'name'=>'桂林');
$data[] =array('id'=>8,'parentid'=>6,'name'=>'南寧');
$data[] =array('id'=>9,'parentid'=>6,'name'=>'柳州');
$data[] =array('id'=>10,'parentid'=>2,'name'=>'紐約');
$data[] =array('id'=>11,'parentid'=>2,'name'=>'華盛頓');
$data[] =array('id'=>12,'parentid'=>3,'name'=>'首爾');

 /**格式化數(shù)組輸出**/
function p($arr)
{
    echo "<pre>";
    echo '========================開始========================';
    echo "</br>";
    if( $arr ){
        print_r($arr);
    } else {
        echo '此值為空';
    }
    echo "</br>";
    echo '========================結(jié)束========================';
    echo "</pre>";
}

/**
 * 多維數(shù)組樹形結(jié)構(gòu)
 */
function tree($data, $pid = 0)
{
    // static $html = '';
    // $html .= '<ul>';
    $children = [];
    // p($data);
    foreach ($data as $key => $value) {

        if ($value['parentid'] == $pid) {
            // $html .= '<li>';
            $children[] = $value;
        }
    }
    if (empty($children)) {
        return null;
    }

    foreach ($children as $key => $value) {
        $chid = tree($data, $value['id']);
        if ($chid != null) {
            $children[$key]['childs'] = $chid;
        }
    }

    // $html .= '</ul>';
    return $children;
}


function creatHtmlTree($tree)
{
    static $htmlTree;
    $htmlTree .= '<ul>';
    foreach ($tree as $key => $value) {
        $htmlTree .= "<li><span><i class='icon-folder-open'></i>{$value['name']} </span> <a href=''>Goes somewhere</a>";
        if (isset($value['childs']) && is_array($value['childs'])) {
            $html = creatHtmlTree($value['childs']);
            $htmlTree .= $html;
        } 
        $htmlTree .= "</li>";
    }
    $htmlTree .= "</ul>";
    return $htmlTree;
}


$tree = tree($data);
$htmlTree = creatHtmlTree($tree);

p($tree);
p($htmlTree);