Get TreeViewItem for TreeView logical element

Question

My tree view seems like this

<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>

In ArticlesTreeView.SelectedItem stores instance of classes NewsPaperDocument, NewsPaperPage, etc. How can I get TreeViewItem associated with SelectedItem? I try to use VisualTreeHelper.GetParent(elem);, but SelectedItem doesn't has type DependencyObject

UPD1 Add simple sample, that demonstrate problem. item in ArticlesTreeView_SelectedItemChanged always 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; }
    }
}

Answer 1

if I got you correctly you want to retrieve the TreeViewItem from the SelectedItem

so you can make use of ItemContainerGenerator

        ItemContainerGenerator gen = ArticlesTreeView.ItemContainerGenerator;
        TreeViewItem item = gen.ContainerFromItem(ArticlesTreeView.SelectedItem) as TreeViewItem;

Get TreeViewItem from nested items

due to the reason that every TreeViewItem has it's own ItemContainerGenerator so in order to find the container from the nested items we need to recurse the depth of the tree

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

    private static TreeViewItem ContainerFromItem(ItemContainerGenerator containerGenerator, object item)
    {
        TreeViewItem container = (TreeViewItem)containerGenerator.ContainerFromItem(item);
        if (container != null)
            return container;

        foreach (object childItem in containerGenerator.Items)
        {
            TreeViewItem parent = containerGenerator.ContainerFromItem(childItem) as TreeViewItem;
            if (parent == null)
                continue;

            container = parent.ItemContainerGenerator.ContainerFromItem(item) as TreeViewItem;
            if (container != null)
                return container;

            container = ContainerFromItem(parent.ItemContainerGenerator, item);
            if (container != null)
                return container;
        }
        return null;
    }