解析出XML后（已经得到data）但find不出值？

xml文件如下
<?xml version="1.0" encoding="UTF-8"?>
<students><student></student></students>
我的jquery是这样写的
$('#letter-d .button').click(
                        function(){
                            $.get('d2.xml',
                                function(data){
                                    alert(data);
                                    $(data).find('student').each(
                                        function(){
                                            alert("aa");
                                        }
                                    );
                                }
                            );
                        }
                    );
能alert出data中的所有值，但我却不能进each，请教原因

真是太奇怪了，我把XML的顶级标签改成<a>就行了。
<a><student></student><a>这样就能进入each
而<students><student></student><students>却不行，这是为什么呢