How to avoid duplicate using Mongodb c++

I have a unique index in MongoDB to avoid duplicates.

I am trying to convert simple code from java to c ++ here is my code to insert documents into MongoDB. codes are working perfectly but when I try to insert same documents application stop working.

     mongocxx::client conn{ mongocxx::uri{ "mongodb://localhost:27017" } };
     mongocxx::write_concern writeConcern;
     writeConcern.acknowledge_level(mongocxx::write_concern::level(1));

    QFile inputFile(path);
   if (inputFile.open(QIODevice::ReadOnly))
    {
    QTextStream in(&inputFile);
    while (!in.atEnd())
    {
        bsoncxx::builder::stream::document document{};
        auto collection = conn["TestDB"]["fdevices"];
        QString line = in.readLine();
        std::string utf8_text = line.toUtf8().constData();
        document << "Data" << utf8_text;

    collection.insert_one(document.view());
        }
    inputFile.close();
     }

here is the code that I used in java. in java, i can simply ignore duplicates by using mongoClient.setWriteConcern(new WriteConcern(0, 10)); and continue my loop to next document.

    MongoClient mongoClient = new MongoClient(asList( new ServerAddress(host+":"+port)), 
        singletonList(MongoCredential.createScramSha1Credential(uname.getText(),
        MongoClientOptions.builder().serverSelectionTimeout(2000)
                                                          .build());
        mongoClient.setWriteConcern(new WriteConcern(0, 10));
        DB db = mongoClient.getDB(dblist.getSelectedValue().toString());
        DBCollection bookCollection = db.getCollection(collectionss.getSelectedValue().toString());
        for (int i = 0; i <sixe; i++) {
            server.prolab.setText("Uploaded files: "+i+" Total files: "+sixe);
            BasicDBObject doc = new BasicDBObject("Data",dataList.getModel().getElementAt(i));
            bookCollection.insert(doc);
        }