How to remove an item from the context menu in WinForms TabbedMDIManager?

public class CustomTabbedMDIManager : TabbedMDIManager
{
   public CustomTabbedMDIManager() : base() {}
   protected override void ContextMenu_BeforePopup(object sender, CancelEventArgs e)
   {
       ParentBarItem popupMenuParentBarItem = sender as ParentBarItem;
       foreach(BarItem bitem in popupMenuParentBarItem.Items)
       {
          if (bitem.Text == "New Hori&zontal Tab Group")
          {
             // To remove the item
             popupMenuParentBarItem.Items.Remove(bitem);
             break;
          }
       }
       base.ContextMenu_BeforePopup(sender, e);
   }
}

Public Class CustomTabbedMDIManager : Inherits TabbedMDIManager
   Public Sub New()
       MyBase.New()
   End Sub
   Protected Overrides Sub ContextMenu_BeforePopup(ByVal sender As Object, ByVal e As CancelEventArgs)
       Dim popupMenuParentBarItem As ParentBarItem = CType(IIf(TypeOf sender Is ParentBarItem, sender, Nothing), ParentBarItem)
       For Each bitem As BarItem In popupMenuParentBarItem.Items
          If bitem.Text = "New Hori&zontal Tab Group" Then
             ' To remove the item
             popupMenuParentBarItem.Items.Remove(bitem)
             Exit For
          End If
       Next bitem
       MyBase.ContextMenu_BeforePopup(sender, e)
    End Sub
End Class