element ui"s three-level navigation menu. When you click on any second-level navigation, all three-level navigation will be expanded 
  
 
 as shown in the figure, when I click on a secondary menu such as a camera, both the wifi and the camera submenus will expand or close the 
 code section: 
< template VFF = "item in items" >
                        <el-submenu :index="item.index">
                            <template slot="title">
                                <img :src="item.icon" alt="">{{ item.title }}
                            </template>
                            <template v-for="(subItem,i) in item.subs" >
                                    <template v-if="subItem.sonSubs">
                                        <el-submenu   :index="subItem.index">
                                            <template slot="title">
                                                <img :src=""../../../static/img/"+subItem.mark+".svg"" alt="">{{ subItem.title }}
                                            </template>
                                            <el-menu-item v-for="(sonSubItem,r) in subItem.sonSubs"  :index="sonSubItem.index">
                                                <img :src=""../../../static/img/"+sonSubItem.mark+".svg"" alt="">{{sonSubItem.title}}
                                            </el-menu-item>
                                        </el-submenu>
                                    </template>
                                </template>
                        </el-submenu>
            </template>