Получить TreeViewItem для логического элемента TreeView

Мое представление дерева выглядит так

<TreeView x:Name="ArticlesTreeView" Grid.Column="0" AllowDrop="True">
            <TreeView.Resources>
                <HierarchicalDataTemplate   DataType="{x:Type structure:NewsPaperDocument}" ItemsSource="{Binding Children}">
                    <TextBlock Text="{Binding Name}" Tag="{Binding Object}" FontWeight="Bold" />
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type structure:NewsPaperPage}" ItemsSource="{Binding Children}">
                    <TextBlock Text="{Binding Name}" Tag="{Binding Object}" Foreground="#00a300" />
                </HierarchicalDataTemplate>
                <HierarchicalDataTemplate DataType="{x:Type structure:NewsPaperTitle}" ItemsSource="{Binding Children}">
                    <TextBlock Text="{Binding Name}" Tag="{Binding Object}" Foreground="#da532c" />
                </HierarchicalDataTemplate>
                <DataTemplate DataType="{x:Type structure:NewsPaperBlock}">
                    <TextBlock Text="{Binding Name}" Tag="{Binding Object}" Foreground="#2b5797" />
                </DataTemplate>
            </TreeView.Resources>
        </TreeView>

В ArticlesTreeView.SelectedItem хранится экземпляр классов NewsPaperDocument, NewsPaperPage, etc. Как я могу связать TreeViewItem с SelectedItem? Я пытаюсь использовать VisualTreeHelper.GetParent(elem);, но SelectedItem не имеет типа DependencyObject

UPD1 Добавьте простой образец, демонстрирующий проблему. item в ArticlesTreeView_SelectedItemChanged всегда null

XAML

<Window x:Class="TestTree.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:testTree="clr-namespace:TestTree"
    Title="MainWindow" Height="350" Width="525">
<Grid>
    <TreeView x:Name="ArticlesTreeView" Grid.Column="0" AllowDrop="True" SelectedItemChanged="ArticlesTreeView_SelectedItemChanged">
        <TreeView.Resources>
            <HierarchicalDataTemplate   DataType="{x:Type testTree:A}" ItemsSource="{Binding Children}">
                <TextBlock Text="{Binding Name}" FontWeight="Bold" />
            </HierarchicalDataTemplate>
            <HierarchicalDataTemplate DataType="{x:Type testTree:B}" ItemsSource="{Binding Children}">
                <TextBlock Text="{Binding Name}" Foreground="#00a300" />
            </HierarchicalDataTemplate>
            <DataTemplate DataType="{x:Type testTree:C}">
                <TextBlock Text="{Binding Name}" Foreground="#2b5797" />
            </DataTemplate>
        </TreeView.Resources>
    </TreeView>
</Grid>

CS

using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;

namespace TestTree
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            var a = new A
            {
                Name = "a",
                Children = new List<B>
                {
                    new B
                    {
                        Name = "b1",
                        Children = new List<C>
                        {
                            new C{Name = "c1"},
                            new C{Name = "c2"},
                            new C{Name = "c3"}
                        },
                    },
                    new B
                    {
                        Name = "b2",
                        Children = new List<C>
                        {
                            new C{Name = "c1"},
                            new C{Name = "c2"},
                            new C{Name = "c3"}
                        },
                    },
                    new B
                    {
                        Name = "b3",
                        Children = new List<C>
                        {
                            new C{Name = "c1"},
                            new C{Name = "c2"},
                            new C{Name = "c3"}
                        },
                    }
                }
            };
            ArticlesTreeView.ItemsSource = new List<A> { a };
        }

        private void ArticlesTreeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
        {
            ItemContainerGenerator gen = ArticlesTreeView.ItemContainerGenerator;
            var item = gen.ContainerFromItem(ArticlesTreeView.SelectedItem);
        }
    }

    internal class A
    {
        public string Name { set; get; }

        public List<B> Children { set; get; }
    }

    internal class B
    {
        public string Name { set; get; }

        public List<C> Children { set; get; }
    }

    internal class C
    {
        public string Name { set; get; }
    }
}