代码1与代码2是对照代码，都是实现遍历，但是代码1执行正常，代码2就报错

1.代码1

<a-menu-item v-for="item3 in item2.children" :key="item3.id">
    <MailOutlined /><span>{{item3.name}}</span>
</a-menu-item>

2.代码2

<template v-for="item3 in item2.children">
   <a-menu-item  :key="item3.id">
        <MailOutlined /><span>{{item3.name}}</span>
   </a-menu-item>
</template>

报错：VueCompilerError: key should be placed on the tag.