$group:
{
  _id:'$_id.staffId',
  name: {$first: '$_id.firstName'},
  statuses:
  {
    $push:
    {
      status:'$_id.status',
      count:'$count'
    }
  },
  staffCount: {$sum: '$count'}
}

{
"_id" : "00238061",
"name" : "Kirstie Rachel Wong",
"statuses" : [
    {
        "status" : "Pending",
        "count" : 1.0
    },
    {
        "status" : "Approved",
        "count" : 2.0
    }
],
"staffCount" : 3.0

private List<Bson> createPipeline(String companyCode, String startDate, String endDate, String eventType, List<String> eventConfigIds, String requestType, String staffId, String status) {
    return Arrays.asList(
            match(and(getBsons(companyCode, startDate, endDate, eventConfigIds, requestType, staffId, status)
            )),
            (group("_id", createIdFields(startDate, endDate, eventType))),
            (group("$staffId",
                    first("firstName", "$firstName"),
                    first("lastName", "$lastName"),
                    first("startDate", "$startDate"),
                    first("endDate", "$endDate"),
                    first("eventType", "$eventType"),
                    first("requestType", "$requestType"),
                    push("statuses", createPushFields()),
                    sum("staffCount", "$count")
            )));
}

private DBObject createPushFields() {
    return new BasicDBObject("status","$status").append("count","$count");
}

[
{
    "_id": "00238061",
    "firstName": "Kirstie Rachel Wong",
    "lastName": "Wong",
    "startDate": "2018-01-01T16:30:40Z",
    "endDate": "2018-12-12T16:30:40Z",
    "eventType": "DutySwap",
    "requestType": 0,
    "statuses": [
        {
            "status": [
                "Approved",
                "Approved",
                "Pending"
            ],
            "count": 3
        }
    ],
    "staffCount": 3
}