How to add a new button in the document state of DockingManager?

//The following code shows how the children of the DockingManager had added
<Window x:Class="WpfApplication24.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:syncfusion="http://schemas.syncfusion.com/wpf"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <syncfusion:DockingManager Name="Docking" UseDocumentContainer="True">
            <ContentControl syncfusion:DockingManager.Header="Document1" syncfusion:DockingManager.State="Document"/>
            <ContentControl syncfusion:DockingManager.Header="Document2" syncfusion:DockingManager.State="Document"/>
            <ContentControl syncfusion:DockingManager.Header="Document3" syncfusion:DockingManager.State="Document"/>
</syncfusion:DockingManager>
    </Grid>
</Window>

//The following code snippet explains how the IsNewButtonEnabled property is applied for the tabcontrol
using Syncfusion.Windows.Tools.Controls;
using Syncfusion.Windows.Shared;
namespace WpfApplication24
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            (Docking.DocContainer as DocumentContainer).Loaded += new RoutedEventHandler(MainWindow_Loaded);       
        }
        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
//This code represents the tabcontrol is fetched from the DockingManager            
DocumentTabControl tabcontrol = VisualUtils.FindDescendant(Docking.DocContainer as Visual, typeof(DocumentTabControl)) as DocumentTabControl;
            if (tabcontrol != null)
            {     
//This code shows how the NewButtonEnabled property is set for the tabcontrol           
                tabcontrol.IsNewButtonEnabled = true;
                tabcontrol.NewButtonClick += tabcontrol_NewButtonClick;              
            }
        }
        void tabcontrol_NewButtonClick(object sender, EventArgs e)
        {
            MessageBox.Show("NewButton clicked");
        }   }