<el-tree ref='addtree' :data="data" @check-change="handleCheckChange" show-checkbox node-key="id" default-expand-all :expand-on-click-node="false">
              <span class="custom-tree-node" slot-scope="{ node, data }">
                <span>{{ node.label }}</span>
                <span>{{node.data.id}}
</el-tree>

思路：判斷el-tree是否選擇 ，判斷tree的getCheckedKeys()數組是否有內容

1.給el-tree加ref , addtree

2.自定義校驗

var checkgroups = (rule, value, callback) => {
      let arr = this.$refs.addtree.getCheckedKeys();
      if (arr.length == 0 || !arr) {
        callback(new Error("請選擇系統賬號組"));
      } else {
        callback();
      }
    };