private void LoadOnDemand(ObservableCollection<ArticleCodeModel> codeModels)
        {
            if (m_XamTreeItemParent == null)
            {
                foreach (ArticleCodeModel artCodeModel in codeModels)
                {
                    if (artCodeModel == null) { continue; }
                    
                    XamTreeItem newItem = new XamTreeItem
                    {
                        Header = artCodeModel.Number + ": " + artCodeModel. Description + " (" + artCodeModel.DirectArticlesCount + " / " + artCodeModel.IndirectArticlesCount + ")",
                        DataContext = artCodeModel
                    };
                    
                    if (Application.Current.Resources["AttributingReadyToImageSourceConverter"] == null) { throw new Exception("XamlParseException - AttributingReadyToImageSourceConverter"); }

                    string dataTemplate = @"<DataTemplate xmlns=""http://schemas.microsoft.com/client/2007""> 
                                             <StackPanel Orientation=""Horizontal"">
                                            <ig:XamTreeItem IsEnabled=""{Binding ArticleCodeModel.CodeModel.AttributingReady}"" Loaded=""XamTreeItem_Loaded"" />
                                            <Image Width=""15"" Height=""15"" Margin=""5,0,0,0"" HorizontalAlignment=""Right"" Loaded=""Image_Loaded"" Source=""{Binding ArticleCodeModel.CodeModel.AttributingReady, Converter={StaticResource AttributingReadyToImageSourceConverter}}"" />
                                            </StackPanel>     
                                            </DataTemplate>";

                    newItem.ItemTemplate = (DataTemplate)XamlReader.Load(dataTemplate);

                    XamTreeItem dummyXamTreeItem = new XamTreeItem();
                    dummyXamTreeItem.Visibility = Visibility.Collapsed;
                    newItem.Items.Add(dummyXamTreeItem);

                    newItem.MouseLeftButtonDown += new MouseButtonEventHandler(XamTreeItem_MouseLeftButtonDown);

                    double actualWidth = newItem.ActualWidth + 20;
                    if (m_MinWidth < actualWidth) { m_MinWidth = actualWidth; }

                    Children.Add(newItem);
                   
                    foreach (XamTreeItem xamTreeItem in Children) { xamTreeItem.MinWidth = m_MinWidth;}
                }
            }
            else
            {
                foreach (ArticleCodeModel artCodeModel in codeModels)
                {
                    if (artCodeModel == null) { continue; }
                    ArticleCodeModel parent = m_XamTreeItemParent.DataContext as ArticleCodeModel;
                    if (parent == null) { continue; }
                    if (m_XamTreeItemParent.Items.Count > codeModels.Count) { continue; }

                    XamTreeItem newItem = new XamTreeItem
                    XamTreeItem newItem = new XamTreeItem
                    {
                        Header = artCodeModel.Number + ": " + artCodeModel. Description + " (" + artCodeModel.DirectArticlesCount + " / " + artCodeModel.IndirectArticlesCount + ")",
                        DataContext = artCodeModel
                    };

                    if (Application.Current.Resources["AttributingReadyToImageSourceConverter"] == null) { throw new Exception("XamlParseException - AttributingReadyToImageSourceConverter"); }

                    string dataTemplate = @"<DataTemplate xmlns=""http://schemas.microsoft.com/client/2007""> 
                                             <StackPanel Orientation=""Horizontal"">
                                            <ig:XamTreeItem IsEnabled=""{Binding ArticleCodeModel.CodeModel.AttributingReady}"" Loaded=""XamTreeItem_Loaded"" />
                                            <Image Width=""15"" Height=""15"" Margin=""5,0,0,0"" HorizontalAlignment=""Right"" Loaded=""Image_Loaded"" Source=""{Binding ArticleCodeModel.CodeModel.AttributingReady, Converter={StaticResource AttributingReadyToImageSourceConverter}}"" />
                                            </StackPanel>     
                                            </DataTemplate>";

                    newItem.ItemTemplate = (DataTemplate)XamlReader.Load(dataTemplate);

                    if (m_XamTreeItemParent.Level < 2)
                    {
                        XamTreeItem dummyXamTreeItem = new XamTreeItem();
                        dummyXamTreeItem.Visibility = Visibility.Collapsed;
                        newItem.Items.Add(dummyXamTreeItem);
                    }

                    newItem.MouseLeftButtonDown += new MouseButtonEventHandler(XamTreeItem_MouseLeftButtonDown);

                    double actualWidth = newItem.ActualWidth + 20;
                    if (m_MinWidth < actualWidth) { m_MinWidth = actualWidth; }

                    m_XamTreeItemParent.Items.Add(newItem);
                  
                    foreach (XamTreeItem xamTreeItem in m_XamTreeItemParent.Items) { xamTreeItem.MinWidth = m_MinWidth; }
                 }
            }
            OnNotifyPropertyChanged("Children");
        }