php 无限循环

<?php
    header("Content-type:text/html;charset=utf-8");
    $arr = array(
        array(1, 0, '语文'),
        array(2, 1, '数学'),
        array(3, 0, '英文'),
        array(4, 3, '美术'),

    );
    function xunhuan($pid = 0) {
        global $arr;
        foreach ($arr as $value) {
            if ($value['1'] == $pid) {
                echo $value[2];
                xunhuan($value[0]);
            }
        }
    }
    xunhuan();