el-tree 设置默认选中不起作用

1、原因

先初始化了选中得keys ，后期初始化得树节点无法被设置

2、代码

    <el-tree
        :data="data"
        show-checkbox
        node-key="id"
        :default-checked-keys="selectedArr"       
        @check-change="handleCheckChange"
      >
      </el-tree>

  data() {
    return {
      data: [],
      selectedArr:[],
    };
  },
  methods: {
    handleCheckChange(data, checked, indeterminate) {
      showPointLayer(data.id, checked);
    },
    async initTreeNodes() {
      const { data: res } = await getLayerTreeNodes(); 
      if (res.result.length > 0) {
        this.data.push({
          label: "图层树",
          id: '99',
          children: res.result,
        });
      }

    },
  },
  mounted() {
    //树绑定完数据之后 再初始化选中得数组
    this.initTreeNodes().then(()=>{
        this.selectedArr=   this.data[0].children.map(o=>{
        return o.id
      }) 
    });
  },
};