I'm getting error 

```
duplicate key error index: my.own.$_id_ dup key: { : ObjectId('57d2c4857c137b20e40c633f')

```

this ObjectId is from first insertOne() but second insertOne() command fails can anybody help me in this.
Just learning Java Driver MongoDB

```
import com.mongodb.MongoClient;
import com.mongodb.MongoCredential;
import com.mongodb.ServerAddress;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.sun.org.apache.xml.internal.security.utils.HelperNodeList;
import org.bson.Document;

import java.util.Arrays;

import static com.mongodb.MongoCredential.*;

public class Main {
    public static void main(String[] args){
        //Creating Credential Parameters
        //MongoCredential credential = createScramSha1Credential("root","my","root".toCharArray());
        //MongoClient to connect
        MongoClient mongo = new MongoClient();
        MongoDatabase database = mongo.getDatabase("my");
        MongoCollection<Document> collection = database.getCollection("own");
        Document document = new Document("x",1).append("y",3);
        collection.insertOne(document);
        collection.insertOne(document.append("z",3));
    }
}

```