I'm trying to translate following MongoDB shell query into C# query.

db.col.find({"Details.a":{$elemMatch:{$elemMatch:{DeviceName : /.Name0./}}}});

As you can see $elemMatch is nested into another $elemMatch. This query runs perfectly in shell.
I have no clue how to translate it to C# as driver doesn't accept a filter without a name.
I'm trying following code:

Builders<BsonDocument>.Filter.ElemMatch ("Details.a", Builders<BsonDocument>.Filter.ElemMatch 
(Builders<BsonDocument>.Filter.Regex(Builders<BsonDocument>.Filter.Regex
("DeviceName",new BsonRegularExpression("")))));

No doubt, it didn't worked.
I'm wondering if you guys have any plan to add support to driver to accept filters without name?