基于elementui的Tree虚线，实线绘制，以及懒加载，如图

加减号用的是阿里的矢量图标库。自行去下载  路径：

https://www.iconfont.cn/home/index?spm=a313x.7781069.1998910419.2

<template>
  <div class="content-box">
    <div class="content-top-lable">系统设置</div>
    <div style="padding: 10px 10px;">
      <div style="margin-top: 10px;" class="container">
        <el-tree
            class="tree-line"
            :indent="0"
            node-key="id"
            ref="indexTree"
            :data="data"
            :load="loadNode"
            show-checkbox
            @check-change="handleCheckChange"
            lazy
        ></el-tree>
      </div>
    </div>
  </div>
</template>

<script>
const defaultListQuery = {
  pageNum: 1,
  pageSize: 10,
  keyword: ""
};

import "../icon/iconfont.css";

export default {
  data() {

    return {
      data: [],
      defaultProps: {
        children: 'children',
        label: 'label'
      },
    }
  },
  created() {
    this.getInitData();
  },
  methods: {
    handleCheckChange(data, checked, indeterminate) {
      //得到所有数据
      console.log(this.$refs.indexTree.getCheckedNodes())
      console.log(data, checked, indeterminate);
    },


    loadNode(node, reslove) {
      let that = this;
      if (node.level === 0) {
        reslove(that.data);
      }
      if (node.level >= 1) {
        this.loadNodeChildren(node, reslove);
      }
    },
    async loadNodeChildren(node, reslove) {
      let param = {
        categoryId: node.data.id,
        type: Number(this.cateTabActive)
      };
      let resArr = [];
      resArr.push({
        label: "新增了一条数据",
      });
      resArr.push({
        label: "新增了二条数据",
      });
      // 将得到的子节点，放进去
      this.$refs.indexTree.updateKeyChildren(resArr);
      return reslove(resArr);
    },
    async getInitData() {
      var list = [
        {
          "domainPath": "515445641576227/39873366667377",
          "domainType": "2",
          "domainName": "福山基地",
          "authType": 1,
          "domainId": 39873366667377
        },
        {
          "domainPath": "515445641576227/317724498412849",
          "domainType": "2",
          "domainName": "宝武碳业",
          "authType": 1,
          "domainId": 317724498412849
        },
        {
          "domainPath": "515445641576227/315760572644936",
          "domainType": "2",
          "domainName": "宝武智维",
          "authType": 1,
          "domainId": 315760572644936
        },
        {
          "domainPath": "515445641576227/236239410978728",
          "domainType": "2",
          "domainName": "马钢股份",
          "authType": 1,
          "domainId": 236239410978728
        },
        {
          "domainPath": "515445641576227/560527541336074",
          "domainType": "2",
          "domainName": "梅山基地",
          "authType": 1,
          "domainId": 560527541336074
        },
        {
          "domainPath": "515445641576227/301272106670337",
          "domainType": "2",
          "domainName": "湛江基地",
          "authType": 1,
          "domainId": 301272106670337
        },
        {
          "domainPath": "515445641576227/515445641576264",
          "domainType": "2",
          "domainName": "宝山基地",
          "authType": 1,
          "domainId": 515445641576264
        },
        {
          "domainPath": "515445641576227/367058992",
          "domainType": "2",
          "domainName": "测试基地",
          "authType": 1,
          "domainId": 367058992
        }
      ]
      for (let i = 0; i < list.length; i++) {
        var obj = {
          label: list[i].domainName,
          children: []
        }
        this.data.push(obj);
      }
    }
  }
}
</script>

<style lang="scss">
.tree-line {
  .el-tree-node {
    position: relative;
    padding-left: 16px; // 缩进量
  }

  .el-tree-node__children {
    padding-left: 16px; // 缩进量
  }

  // 竖线
  .el-tree-node::before {
    content: "";
    height: 100%;
    width: 1px;
    position: absolute;
    left: -3px;
    top: -26px;
    border-width: 1px;
    border-left: 1px solid #1867D6;
  }

  // 当前层最后一个节点的竖线高度固定
  .el-tree-node:last-child::before {
    height: 38px; // 可以自己调节到合适数值
  }

  // 横线
  .el-tree-node::after {
    content: "";
    width: 24px;
    height: 20px;
    position: absolute;
    left: -3px;
    top: 12px;
    border-width: 1px;
    border-top: 1px solid #1867D6;
  }

  // 去掉最顶层的虚线，放最下面样式才不会被上面的覆盖了
  & > .el-tree-node::after {
    border-top: none;
  }

  & > .el-tree-node::before {
    border-left: none;
  }

  //收起的图标
  .el-icon-caret-right:before {
    font-size: 18px;
    color: #1867D6;
    content: "\e6fb" !important;
    font-family: "iconfont" !important;
  }

  //展开的图标
  .el-tree-node__expand-icon.expanded.el-icon-caret-right:before {
    font-size: 18px;
    content: "\e6fd" !important;
    color: #1867D6;
    font-family: "iconfont" !important;

    &.is-leaf {
      color: transparent;
      // display: none; // 也可以去掉
    }
  }

  // 最后没有子节点不展示图标
  .el-tree-node__expand-icon.is-leaf::before {
    background: #fff;
    content: '' !important;
    font-family: '' !important;
    display: block;
    width: 0px;
    height: 0px;
    font-size: 16px;
    background-size: 16px;
  }

}
</style>