Pymongo overwrites data when I use update_one Python [duplicate]

Question

I'm trying to solve an issue in Pymongo. I have a dictionary like this :

{
  "_id": 6,
  "engineers": {
    "1": {
      "name": "George ",
      "hours": "2"
    }
  }
}

And I want to insert another record inside the field engineers:

{
  "_id": 6,
  "engineers": {
    "1": {
      "name": "George ",
      "hours": "2"
    }
    "2": {
      "name": "Spyros",
      "hours": "12"
    }
  }
}

I use the update command :

   dic =   "2": {
          "name": "Spyros",
          "hours": "12"
        }
   x = mydb.mycollection.update_one({ "_id": "6" },{ "$set": {"engineers":dic} })

However, this command overwrites the previous data!

Any help, please?