element-plus/docs/examples/tree/custom-leaf.vue

<template>
  <el-tree :props="props" :load="loadNode" lazy show-checkbox />
</template>

<script lang="ts">
export default {
  data() {
    return {
      props: {
        label: 'name',
        children: 'zones',
        isLeaf: 'leaf',
      },
    }
  },
  methods: {
    loadNode(node, resolve) {
      if (node.level === 0) {
        return resolve([{ name: 'region' }])
      }
      if (node.level > 1) return resolve([])

      setTimeout(() => {
        const data = [
          {
            name: 'leaf',
            leaf: true,
          },
          {
            name: 'zone',
          },
        ]

        resolve(data)
      }, 500)
    },
  },
}
</script>