WPF TreeView nesting types of same class

Question

EDIT AFTER CLOSE

Thanks for that partial answer. It was a valid suggestion. Although I don't believe my question had to be closed for that. I added a getter and setter to the immutable field, and now the treeview loads the root node, and ONE level of subnodes (public List<AdOu> Items { get; set; } = new List<AdOu>();) Still... as was the original intent of my question, I believe the HierarchicalDataTemplate doesn't work for Items on level 3 and below.

ORIGINAL QUESTION

I'm trying to recreate the Active Directory (Organizational Units) in a TreeView control. The following is one of the things I tried already.

    <Window.Resources>
        <DataTemplate x:Key="treeviewou">
            <TextBlock Text="{Binding Name}" />
        </DataTemplate>
        <HierarchicalDataTemplate 
            x:Key="treeviewitems" 
            DataType="{x:Type admodels:AdOu}" 
            ItemsSource="{Binding Items}"
            ItemTemplate="{StaticResource treeviewou}">
            <StackPanel>
                <TextBlock Text="{Binding Name}" />
            </StackPanel>
        </HierarchicalDataTemplate>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="83*"/>
            <ColumnDefinition Width="317*"/>
        </Grid.ColumnDefinitions>
        <DataGrid x:Name="grdUsers" Grid.Column="1" d:ItemsSource="{d:SampleData ItemCount=5}"/>
        <TreeView x:Name="tvOus"
                  SelectedItemChanged="tvOus_SelectedItemChanged"
                  ItemTemplate="{StaticResource treeviewitems}"
                  >
            
        </TreeView>
    </Grid>

DataType="{x:Type admodels:AdOu}" looks like this:

    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.DirectoryServices;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    namespace ADUtils.Models
    {
        public class AdOu : ViewModelBase
        {
            private SearchResult? _searchResult;
            private DirectoryEntry? _directoryEntry;
            private string? _name;
            public List<AdOu> Items { get; set; } = new List<AdOu>();

            public AdOu(SearchResult sr)
            {
                searchResult = sr;
                //Text = sr.Properties["name"][0].ToString();
            }
            public AdOu(DirectoryEntry de) {
                directoryEntry = de;
                //Text = de.Properties["name"][0].ToString();
            }
            public SearchResult? searchResult {
                get {
                    if (_searchResult == null && directoryEntry != null) {
                        DirectoryEntry startingPoint = new DirectoryEntry(directoryEntry.Path);

                        DirectorySearcher searcher = new DirectorySearcher(startingPoint);
                        searcher.SearchScope = SearchScope.Base;
                        //searcher.Filter = "(objectCategory=organizationalUnit)";

                        _searchResult = searcher.FindOne();
                    }
                    return _searchResult;
                }
                set {
                    _searchResult = value;
                    OnPropertyChanged(nameof(Name));
                }
            }
            public DirectoryEntry? directoryEntry {
                get {
                    if (_directoryEntry == null && searchResult != null) {
                        _directoryEntry = searchResult.GetDirectoryEntry();
                    }
                    return _directoryEntry;
                     
                }
                set {
                    _directoryEntry = value;
                    OnPropertyChanged(nameof(Name));
                }
            }
            public string? Name {
                get {
                    if (_name == null && searchResult != null && searchResult.Properties["Name"].Count > 0) {
                        _name = searchResult.Properties["Name"][0].ToString();
                    }
                    return _name;
                }
            }
        }
    }

PS. ViewModelBase holds my OnPropertyChanged logic

Next, I create the OU hierarchy and bind it to the treeview

    public void InitTreeView() {
        ListOus = adOUs.GetHierarchical();
        //ListTreeViewItems = new ObservableCollection<ADTreeViewItem>();
        TreeViewList = new ObservableCollection<AdOu>(ListOus);
        tvOus.ItemsSource = TreeViewList;
        //foreach (AdOu ou in ListOus) {
        //    ListTreeViewItems.Add(OusToTreeView(ou));
        //}
        //tvOus.ItemsSource = ListTreeViewItems;
    }
    private ADTreeViewItem OusToTreeView(AdOu? ou = null, ADTreeViewItem? parent = null) {
        ADTreeViewItem tviRoot = new ADTreeViewItem(ou);
            
        foreach (AdOu child in ou?.Items ?? ListOus ?? new List<AdOu>()) {
            OusToTreeView(child, tviRoot);
        }
        if (parent != null) {
            parent.Items.Add(tviRoot);
        }
        return tviRoot;
    }

Sidenote The commented out lines in the InitTreeView function is what I had tried before. The treeview loaded those nodes, but didn't display the text. Since you shouldn't override the TreeViewItem class according to 'the internet', I gave up on that approach.

Current approach I know this example is wrong, this example only loads the first node (top-root node), without loading the child nodes. I think it's because It doesn't recognize the child's HierarchicalDataTemplate it has to use.

I really don't know how to solve this. The entire hierarchy tree exists out of AdOu objects with it's respective List<AdOu> items. This question's answer may help, but I don't understand how to implement it, and if it would work.