element-plus/docs/examples/tree/default-state.vue

<template>
  <el-tree
    :data="data"
    show-checkbox
    node-key="id"
    :default-expanded-keys="[2, 3]"
    :default-checked-keys="[5]"
    :props="defaultProps"
  />
</template>

<script lang="ts">
export default {
  data() {
    return {
      data: [
        {
          id: 1,
          label: 'Level one 1',
          children: [
            {
              id: 4,
              label: 'Level two 1-1',
              children: [
                {
                  id: 9,
                  label: 'Level three 1-1-1',
                },
                {
                  id: 10,
                  label: 'Level three 1-1-2',
                },
              ],
            },
          ],
        },
        {
          id: 2,
          label: 'Level one 2',
          children: [
            {
              id: 5,
              label: 'Level two 2-1',
            },
            {
              id: 6,
              label: 'Level two 2-2',
            },
          ],
        },
        {
          id: 3,
          label: 'Level one 3',
          children: [
            {
              id: 7,
              label: 'Level two 3-1',
            },
            {
              id: 8,
              label: 'Level two 3-2',
            },
          ],
        },
      ],
      defaultProps: {
        children: 'children',
        label: 'label',
      },
    }
  },
}
</script>