In the below code I have created Menu Groups. Simply I have added menu items in menu folder, all menu item are added in group. See the below code it will clearly described how to make Menu Groups .

Step(1)-MainActivity-

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

Step(2)-Added menu items in Menu folder-

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android" >

    <item
        android:id="@+id/menu_bookmark"
        android:icon="@drawable/icon_bookmark"
        android:title="Read"/>
    <!-- menu group -->
    <group android:id="@+id/group_delete" >
        <item
            android:id="@+id/menu_more"
            android:title="write"/>

         <item
            android:id="@+id/menu_delete"
            android:title="Save"/>
        <item
            android:id="@+id/menu_delete"
            android:title="Delete"/>
    </group>

</menu>