函数从任何地方输出数组0个元素

函数的输出看起来不错，但我每次都从任何地方获得额外的[0] => Array ( [1] => 1 )。id从我的db表中的1开始。0是从哪里来的?!

Array ( [1] => Array ( [name] => Sual [parent] => 0 ) **[0] => Array ( [1] => 1 )** ...

函数

<?php
function treeGen($menu, $utype) {
    global $db;
    $tree = array();
    $stmt = $db->prepare("select id, parent, name FROM navigation WHERE menu=? AND user_type=?") or die($db->error);
    $stmt->bind_param("ii", $menu, $utype) or die($stmt->error);
    $stmt->execute() or die($stmt->error);
    $stmt->store_result();
    $meta = $stmt->result_metadata();
    $stmt->bind_result($id, $parent, $name);
    while ($stmt->fetch()) {
        $tree[$id] = array(
            'name' => $name, 
            'parent' => $parent
        );
        if (!array_key_exists($parent,$tree)) {
            $tree[$parent][$id] = $id;
        }
    }
    $stmt->close();
   print_r($tree);
}
?>