mongodb – insert multiple documents in a single query with only 1 field distinct | MONGO

I want to insert multiple documents in a collection, but the difference in each one of them is only one field. The documents schema looks something like this:

{
"_id": {
        "variant": "A",
        "abc": "def",
       },
       "pqr": "mno",
       ...
    }
}

in the above, only the "_id.variant" field is distinct in each of the documents to be inserted. Is there any way I can insert it with a single query for variants ranging from "A", "B", "C", "D" ... "Z".?