Auto-Delete Certain type of Document in Mongodb in collection

Working with Data Drivers
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3

I get "UploadTimeType" : "string".

So I guess UploadTime is not type: Date.
How do I insert UploadTime as type Date?

I tried the following it didn’t work:

BsonDateTime uploadDate = new BsonDateTime(DateTime.Now);
var doc = new BsonDocument{
                         {"Documentid", strDocumentID},
                         { "FileType", typeOfDocument},                                        
                         { "FileContent", file.ContentType},
                         { "FileName", file.FileName},
                         { "UploadTime", uploadDate },
                         { "UploadedBy", uploadedBy},
                         { "GridFSFileID", strGridFSFileID}
                       };

This did not work.