https://mongodb.github.io/mongo-csharp-driver/2.15/apidocs/html/M_MongoDB_Bson_Serialization_BsonSerializer_Deserialize_4.htm
BsonSerializer.Deserialize Method (TextReader, Type, Action(BsonDeserializationContext.Builder))
Deserializes an object from a JSON TextReader.
methodtypeactionbuilder
https://mongodb.github.io/mongo-csharp-driver/2.14/apidocs/html/P_MongoDB_Bson_Serialization_BsonDeserializationContext_Builder_AllowDuplicateElementNames.htm
BsonDeserializationContext.Builder.AllowDuplicateElementNames Property
Gets or sets a value indicating whether to allow duplicate element names.
builderproperty