Retrofit show json Response in ListView very easy and short

public class MainActivity extends AppCompatActivity {

    TextView tv;

    ListView listView;

    List<String> stringList = new ArrayList<>();

    public static final String Root_url = "http://echo.jsontest.com/";

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        tv = (TextView) findViewById(R.id.tv_response);

        listView = (ListView) findViewById(R.id.listview);

        insertUser();

        ArrayAdapter<String> stringArrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, stringList);

        listView.setAdapter(stringArrayAdapter);

    }

    private void insertUser() {

        RestAdapter adapter = new RestAdapter.Builder().setEndpoint(Root_url).build();

        DetailsAPI api = adapter.create(DetailsAPI.class);

        api.insertUser(new Callback<JsonObject>() {

            @Override

            public void success(JsonObject jsonObject, Response response) {

                if (response.getStatus() == 200)

                    tv.setText("You got the data");

                String jsonResponse = jsonObject.get("one").getAsString();

                stringList.add(jsonResponse);

                jsonResponse = jsonObject.get("key").getAsString();

                stringList.add(jsonResponse);

                //*********************Json response  is too short so the same above values are stored in list array repeatedly.... **************

                jsonResponse = jsonObject.get("one").getAsString();

                stringList.add(jsonResponse);

                jsonResponse = jsonObject.get("key").getAsString();

                stringList.add(jsonResponse);

                jsonResponse = jsonObject.get("one").getAsString();

                stringList.add(jsonResponse);

                jsonResponse = jsonObject.get("key").getAsString();

                stringList.add(jsonResponse);

            }

            public void failure(RetrofitError error) {

                Toast.makeText(MainActivity.this, "try again!", Toast.LENGTH_SHORT).show();

            }

        });

    }

}

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    tools:context=".MainActivity">

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Hello Response here"

        android:textColor="#ff2323"

        android:textSize="22sp"

        android:id="@+id/tv_response" />

    <ListView

        android:id="@+id/listview"

        android:layout_below="@+id/tv_response"

        android:layout_width="match_parent"

        android:layout_height="100dp">

    </ListView>

</RelativeLayout>