一、页面渲染好tree

<template>
    <div class='mytree'>
        <el-tree :data="data" :indent='0' :props="defaultProps" @node-click="handleNodeClick"> 
        </el-tree>
    </div>
</template>

注意：   ：indent='0'这一项设置一下，否则线跟节点之间会有很大的缝隙

二、写样式

<style lang="scss" scoped>
.mytree /deep/{
     .el-tree > .el-tree-node:after {
      border-top: none;
    }
    .el-tree-node {
      position: relative;
      padding-left: 16px;
    }
    //节点有间隙，隐藏掉展开按钮就好了,如果觉得空隙没事可以删掉
    .el-tree-node__expand-icon.is-leaf{
      display: none;
    }
    .el-tree-node__children {
      padding-left: 16px;
    }

    .el-tree-node :last-child:before {
      height: 38px;
    }

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

    .el-tree > .el-tree-node:after {
      border-top: none;
    }

    .el-tree-node:before {
      content: "";
      left: -4px;
      position: absolute;
      right: auto;
      border-width: 1px;
    }

    .el-tree-node:after {
      content: "";
      left: -4px;
      position: absolute;
      right: auto;
      border-width: 1px;
    }

    .el-tree-node:before {
      border-left: 1px dashed #4386c6;
      bottom: 0px;
      height: 100%;
      top: -26px;
      width: 1px;
    }

    .el-tree-node:after {
      border-top: 1px dashed #4386c6;
      height: 20px;
      top: 12px;
      width: 24px;
    }
  }
<style>

效果图：

感谢：这篇博客

https://blog.csdn.net/u011225228/article/details/93141026