using MongoDB.Bson;

using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        BsonDocument[] data = new BsonDocument[]{new BsonDocument{{"_id", "1"}, {"name", "name_1"}, {"description", "description_1"}, }, new BsonDocument{{"_id", "2"}, {"name", "name_2"}, {"description", "description_2"}, }, new BsonDocument{{"_id", "3"}, {"name", "name_3"}, {"description", "description_3"}, }};

        var kvp = data.AsEnumerable()

            .ToDictionary(x => x["_id"], x => new { name = x["name"], description = x["description"] });

        Console.WriteLine(kvp.ToJson());

        // Cast to BsonDocument

        var bsonDoc = kvp.ToBsonDocument();

        Console.WriteLine(bsonDoc);

    }

}