Elasticsearch Collapse and Inner_hits

desired_output.json

{
  "took": 11,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 12,
    "max_score": null,
    "hits": [
      {
        "_index": "employees",
        "_type": "_doc",
        "_id": "9",
        "_score": null,
        "_source": {},
        "fields": {
          "city": [
            "Amsterdam"
          ]
        },
        "sort": [
          "Amsterdam"
        ],
        "inner_hits": {
          "order by age": {
            "hits": {
              "total": 2,
              "max_score": null,
              "hits": [
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "11",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 11",
                    "city": "Amsterdam",
                    "age": 44
                  },
                  "sort": [
                    44
                  ]
                },
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "9",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 09",
                    "city": "Amsterdam",
                    "age": 40
                  },
                  "sort": [
                    40
                  ]
                }
              ]
            }
          }
        }
      },
      {
        "_index": "employees",
        "_type": "_doc",
        "_id": "1",
        "_score": null,
        "_source": {},
        "fields": {
          "city": [
            "Chicago"
          ]
        },
        "sort": [
          "Chicago"
        ],
        "inner_hits": {
          "order by age": {
            "hits": {
              "total": 5,
              "max_score": null,
              "hits": [
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "12",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 12",
                    "city": "Chicago",
                    "age": 46
                  },
                  "sort": [
                    46
                  ]
                },
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "8",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 08",
                    "city": "Chicago",
                    "age": 38
                  },
                  "sort": [
                    38
                  ]
                }
              ]
            }
          }
        }
      },
      {
        "_index": "employees",
        "_type": "_doc",
        "_id": "10",
        "_score": null,
        "_source": {},
        "fields": {
          "city": [
            "Madrid"
          ]
        },
        "sort": [
          "Madrid"
        ],
        "inner_hits": {
          "order by age": {
            "hits": {
              "total": 1,
              "max_score": null,
              "hits": [
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "10",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 10",
                    "city": "Madrid",
                    "age": 42
                  },
                  "sort": [
                    42
                  ]
                }
              ]
            }
          }
        }
      },
      {
        "_index": "employees",
        "_type": "_doc",
        "_id": "2",
        "_score": null,
        "_source": {},
        "fields": {
          "city": [
            "San Francisco"
          ]
        },
        "sort": [
          "San Francisco"
        ],
        "inner_hits": {
          "order by age": {
            "hits": {
              "total": 4,
              "max_score": null,
              "hits": [
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "5",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 05",
                    "city": "San Francisco",
                    "age": 32
                  },
                  "sort": [
                    32
                  ]
                },
                {
                  "_index": "employees",
                  "_type": "_doc",
                  "_id": "4",
                  "_score": null,
                  "_source": {
                    "employee": "Emp 04",
                    "city": "San Francisco",
                    "age": 30
                  },
                  "sort": [
                    30
                  ]
                }
              ]
            }
          }
        }
      }
    ]
  }
}