title: Element UI Tree Data not updating with Vue
body: <p>I have created following vue component. </p>
  
  <p>Following code is not updating data when I update after ajax response. </p>
  
  <p>Is there any specific method I need to apply after updating data. </p>
  
  <p>I am using class based vue cli 3 components. It is not giving any error also. Just data is not updating. </p>
  
  <p>Is there any method we need to use for vue reactivity to update the data or mounted event don't work?</p>
  
  <p>Even if I give empty array as children, Name is not updating.</p>
  
  <pre><code>&lt;template&gt;
        &lt;el-tree :data="MyData" :props="defaultProps"&gt;&lt;/el-tree&gt;
  &lt;/template&gt;
  
  &lt;script lang="ts"&gt;
  import { Component, Vue } from 'vue-property-decorator';
  import ElemUI from 'element-ui';
  import axios from 'axios';
  
  @Component({
    components: {
      ElTree: ElemUI.Tree,
    },
  })
  export default class In extends Vue {
    public MyData: any = [
            {
              label: 'Data',
              children: [],
            },
          ];
    public defaultProps: any = {
      children: 'children',
      label: 'label',
    };
    public mounted() {
      axios
        .post('https://localhost:44375/api/Graph', {
          query: `{
                  myData {
                      name,
                      innerData {
                      name
                      }
                    }
                  }`,
        })
        .then((response) =&gt; {
          this.MyData = [
            {
              label: 'Another Data',
              children: Response.data.data.AnotherArrayData
            },
          ];
        });
    }
  }
  &lt;/script&gt;
  </code></pre>