let arr = [
{
  name:小七,
  id:1
},
{
  name:小八,
  id:2
},
{
  name: 小九,
  id:3
}
]

let menuItems = [
{
  name:小七,
  id:1,
  children:[
    {
      name: '啥也不是',
      pid:2
    }
  ]
},
{
  name:小八,
  id:2,
  children:[
    {
      name:'随便写哦',
      pid:3,
      children:[
        {
          name: '再次深入',
          pid: 4,
          children:[
            {
              name: '撒打算',
              pid:666
            }
          ]
        }
      ]
    }  
  ]
},
{
  name: 小九,
  id:3
}
]

computed: {
  treeData() {
   let cloneData = JSON.parse(JSON.stringify(this.tableData)); // 对源数据深度克隆
   return cloneData.filter(father => {
    let branchArr = cloneData.filter(child => father.id == child.pid); //返回每一项的子级数组
    branchArr.length > 0 ""; //如果存在子级，则给父级添加一个children属性，并赋值
    return father.pid == 0; //返回第一层
   });
  }
 },

<el-menu
    background-color="#304156"
    text-color="#fff"
    active-text-color="#409eff"
    :collapse="isActive"
    :collapse-transition="false"
    :unique-opened="true"
    :router="true"
    :default-active="activePath"
   >
    <menu-tree :menuData="treeData" @saveNavStart="saveNavStart"></menu-tree>
   </el-menu>
   
   这里的激活样式用的是缓存的办法
   // 保存链接的激活状态
  saveNavStart(activePath) {
   window.sessionStorage.setItem("activePath", activePath);
   this.activePath = activePath;
  },
  created() {
    this.activePath = window.sessionStorage.getItem("activePath");
  }

<template>
 <div>
  <label v-for="menu in menuData" :key="menu.id">
   <el-submenu :index="String(menu.id)" v-if="menu.children">
    <template slot="title">
     <i class="el-icon-edit"></i>
     <span>{{menu.menu_name}}</span>
    </template>
    <label>
     <menutree :menuData="menu.children"></menutree>
    </label>
   </el-submenu>
   <el-menu-item :index="menu.path" @click="saveNavStart(menu.path)" v-else>
    <i class="el-icon-edit"></i>
    <span>{{menu.menu_name}}</span>
   </el-menu-item>
  </label>
 </div>
</template>

methods:{
  saveNavStart(activePath) {
    this.$emit('saveNavStart',activePath)
  }
  }
}