OUViewModel.cs

public class OUViewModel : TreeViewItemViewModel
    {
        readonly DirectoryEntry _de;
        private Stack<string> searchStack = new Stack<string>();

        public OUViewModel(DirectoryEntry de, OUViewModel parent)
            // The DirectorySearcher here is checking to see if there are any children under this DirectoryEntry
            : base(parent, new DirectorySearcher(de, "(objectClass=organizationalUnit)", null, SearchScope.OneLevel).FindOne() != null)
        {
            _de = de;
        }
        
        public string Name
        {
            get { return _de.Name.Substring(_de.Name.IndexOf('=') + 1); }
        }

        public string Path
        {
            get { return _de.Path; }
        }

        protected override void LoadChildren()
        {
            MainWindow.StartProgressBar();
            BackgroundWorker childLoader = new BackgroundWorker();
            childLoader.DoWork += GetChildren;
            childLoader.RunWorkerCompleted += UpdateChildren;
            childLoader.RunWorkerAsync(this);
        }

        private void GetChildren(object sender, DoWorkEventArgs e)
        {
            OUViewModel parent = e.Argument as OUViewModel;
            DirectoryEntry parentDE = parent._de;
            DirectorySearcher searcher = new DirectorySearcher(parentDE, "(objectClass=organizationalUnit)")
            {
                // SearchScope = OneLevel means the searcher will return its children when using FindOne() or FindAll()
                SearchScope = SearchScope.OneLevel
            };
            ObservableCollection<OUViewModel> children = new ObservableCollection<OUViewModel>();
            foreach (SearchResult result in searcher.FindAll())
            {
                children.Add(new OUViewModel(result.GetDirectoryEntry(), parent));
            }
            e.Result = children;
        }

        private void UpdateChildren(object sender, RunWorkerCompletedEventArgs e)
        {
            foreach (OUViewModel child in e.Result as ObservableCollection<OUViewModel>)
            {
                child.Search(searchStack);
                Children.Add(child);
            }
            MainWindow.StopProgressBar();
        }

        #region Custom Methods

        public void Search(Stack<string> path)
        {
            searchStack = path;
            if (searchStack.Count > 0)
            {
                // Let's see if our current OU is next in the path
                string name = searchStack.Peek();
                if (Name == name)
                {
                    searchStack.Pop();
                    IsExpanded = true;
                    if (HasLoadedChildren)
                    {
                        foreach (OUViewModel child in Children)
                        {
                            child.Search(searchStack);
                        }
                    }
                    else
                    {
                        LoadChildren();
                    }
                    if (searchStack.Count == 0)
                    {
                        IsSelected = true;
                    }
                }
            }
        }

        #endregion
    }