效果如图所示：

 1.新建el-select-tree.vue组件

<!--
 * 下拉树形选择
-->
<template>
    <el-select ref="selectTree" :value="value" v-model="valueName" :multiple="multiple" :clearable="clearable"
        @clear="clearHandle" @change="changeValue">
        <el-option :value="valueName" class="options">
            <el-tree id="tree-option" ref="selectTree" :accordion="accordion" :data="options" :props="props"
                :node-key="props.value" @node-click="handleNodeClick">
                <span slot-scope="{ data }">
                    <i :class="[data.color != null ? 'ification_col' : '']"
                        :style="{ 'background-color': data.color }"></i>&nbsp;&nbsp;{{ data.name }}
                </span>
            </el-tree>
        </el-option>
    </el-select>
</template>
<script>
export default {
    name: "el-tree-select",
    props: {
        // 配置项
        props: {
            type: Object,
            default: () => {
                return {
                    value: 'id',
                    children: 'children',
                    label: 'name'
                }
            }
        },
        // 选项列表数据(树形结构的对象数组)
        options: {
            type: Array,
            default: () => {
                return []
            }
        },
        // 初始值（单选）
        value: {
            type: Object,
            default: () => {
                return {}
            }
        },
        // 初始值（多选）
        valueMultiple: {
            type: Array,
            default: () => {
                return []
            }
        },
        // 可清空选项
        clearable: {
            type: Boolean,
            default: true
        },
        // 自动收起
        accordion: {
            type: Boolean,
            default: false
        },
        // 是否多选
        multiple: {
            type: Boolean,
            default: false
        }
    },
    data() {
        return {
            resultValue: [], // 传给父组件的数组对象值
            valueName: this.multiple ? [] : '' // 输入框显示值
        }
    },
    watch: {
        value() {
            this.resultValue = this.multiple ? this.valueMultiple : this.value;   // 初始值
            this.initHandle()
        }
    },
    mounted() {
        this.resultValue = this.multiple ? this.valueMultiple : this.value;   // 初始值
        this.initHandle();
    },
    methods: {
        // 初始化显示
        initHandle() {
            if (this.resultValue) {
                if (this.multiple) {
                    // 多选 
                    this.resultValue.forEach(item => this.valueName.push(item.name));
                } else {
                    // 单选
                    this.valueName = this.resultValue.name;
                }
            }
            this.initScroll()
        },
        // 初始化滚动条
        initScroll() {
            this.$nextTick(() => {
                let scrollWrap = document.querySelectorAll('.el-scrollbar .el-select-dropdown__wrap')[0]
                let scrollBar = document.querySelectorAll('.el-scrollbar .el-scrollbar__bar')
                scrollWrap.style.cssText = 'margin: 0px; max-height: none; overflow: hidden;'
                scrollBar.forEach(ele => ele.style.width = 0)
            })
        },
        // 切换选项
        handleNodeClick(node) {
            // 设置点击叶子节点后被选中 可以更改为点击父节点也生效
            if (node.children == null || node.children == undefined) {
                if (this.multiple) {
                    // 多选（判重后添加）
                    let num = 0;
                    this.valueName.forEach(item => {
                        item == node[this.props.label] ? num++ : num;
                    })
                    if (num == 0) {
                        this.valueName.push(node[this.props.label]); // 输入框显示值
                        this.resultValue.push(node);
                    }
                } else {
                    // 单选
                    this.$refs.selectTree.blur();
                    this.valueName = node[this.props.label];
                    this.resultValue = node;
                }

                this.$emit('getValue', this.resultValue);
            }
        },
        // 从输入框中直接删除某个值时
        changeValue(val) {
            if (this.multiple) {
                // 多选（同时删掉传给父组件中多余的值，再传给父组件）
                this.resultValue.map((item, index) => {
                    let i = val.indexOf(item.name)
                    if (i == -1) {
                        this.resultValue.splice(index, 1)
                    }
                })
                this.$emit('getValue', this.resultValue);
            } else {
                // 单选
                this.$emit('getValue', val);
            }
        },
        // 清除选中
        clearHandle() {
            this.valueName = this.multiple ? [] : ''
            this.resultValue = []
            this.clearSelected()
            this.$emit('getValue', this.resultValue)
        },
        // 清空选中样式
        clearSelected() {
            let allNode = document.querySelectorAll('#tree-option .el-tree-node')
            allNode.forEach((element) => element.classList.remove('is-current'))
        }
    }
}
</script>
<style scoped>
.el-scrollbar .el-scrollbar__view .el-select-dropdown__item {
    height: auto;
    max-height: 300px;
    padding: 0;
    overflow: hidden;
    overflow-y: auto;
}

.el-select-dropdown__item.selected {
    font-weight: normal;
}

ul li>>>.el-tree .el-tree-node__content {
    height: auto;
    padding: 0 20px;
}

.el-tree-node__label {
    font-weight: normal;
}

.el-tree>>>.is-current .el-tree-node__label {
    color: #409EFF;
    font-weight: 700;
}

.el-tree>>>.is-current .el-tree-node__children .el-tree-node__label {
    color: #606266;
    font-weight: normal;
}

.el-popper {
    z-index: 9999;
}

.ification_col {
    width: 20px;
    height: 10px;
    display: inline-block;
}
</style>

2.页面引入组件使用

<template>
  <div class="selectTree">
    <label>请选择：</label>
    <!-- 单选 + 默认值 -->
    <!-- <el-select-tree :options="options" :value="value" @getValue="getSelectedValue"></el-select-tree> -->
    <!-- 多选 + 默认值 -->
    <el-select-tree :options="options" :multiple="multiple" :valueMultiple="valueMultiple"
      @getValue="getSelectedValue"></el-select-tree>
  </div>
</template>
<script>
import elSelectTree from '../components/el-select-tree.vue'
export default {
  components: {
    elSelectTree
  },
  data() {
    return {
      // 开启/关 多选/单选
      multiple: true,
      value: {
        id: 3,
        name: '张三'
      },
      valueMultiple: [
        {
          id: 3,
          name: '张三'
        }, {
          id: 4,
          name: '李四'
        }
      ],
      options: [
        {
          id: 1,
          name: '一组',
          children: [{
            id: 2,
            name: '第一队',
            children: [{
              id: 3,
              name: '小张'
            }, {
              id: 4,
              name: '小刘'
            }]
          }]
        },
        {
          id: 5,
          name: '二组',
          children: [{
            id: 6,
            name: '小马'
          }, {
            id: 7,
            name: '小丽'
          }]
        },
        {
          id: 8,
          name: '三组',
          children: [{
            id: 9,
            name: '小韩'
          }, {
            id: 10,
            name: '小钱'
          }]
        }
      ]
    }
  },
  created() {

  },
  methods: {
    // 组件传出来的选中结果
    getSelectedValue(value) {
      console.log('选中的结果值', value)
    }
  }
}
</script>
<style lang="scss"></style>