public abstract class BaseTreeItem : INotifyPropertyChanged
    {
        public static BaseTreeItem LoadingItem = new LoadingItem();
        private bool _isExpanded;
        private bool _isSelected;
        private bool _hasItems;

        protected BaseTreeItem()
        {
            Children = new ObservableCollection<BaseTreeItem>();
        }

        public bool IsSelected
        {
            set
            {
                if (value.Equals(_isSelected)) return;
                _isSelected = value;
                OnPropertyChanged("IsSelected");
            }
            get { return _isSelected; }
        }

        public bool IsExpanded
        {
            set
            {
                if (value.Equals(_isExpanded)) return;

                _isExpanded = value;
                OnPropertyChanged("IsExpanded");

                Children.Clear();
                LoadChildren();
            }
            get { return _isExpanded; }
        }

        public abstract string DisplayName { set; get; }

        public bool HasItems

        {
            set
            {
                if (value)
                {
                    Children.Add(LoadingItem);
                }
                else
                {
                    Children.Clear();
                }
                _hasItems = value;
            }
            get { return _hasItems; }
        }

        public abstract void LoadChildren();

        public BaseTreeItem Paren { set; get; }

        public ObservableCollection<BaseTreeItem> Children { get; set; }

        public event PropertyChangedEventHandler PropertyChanged;

        [NotifyPropertyChangedInvocator]
        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public sealed class LoadingItem : BaseTreeItem
    {
        public override string DisplayName
        {
            get
            {
                return "Loading";
            }
            set
            {
                throw new Exception("Can't change displayname");
            }
        }
        public override void LoadChildren() {}
    }

    public class XmlTreeItem : BaseTreeItem
    {
        private readonly XmlNode _node;

        public XmlTreeItem(XmlNode node)
        {
            _node = node;
            HasItems = _node.ChildNodes.Count > 0;
        }

        public override void LoadChildren()
        {
            foreach (XmlNode i in _node.ChildNodes)
                Children.Add(new XmlTreeItem(i));
        }

        public override string DisplayName
        {
            get
            {
                if (_node == null) return "Null refrense";
                var result = _node.Attributes != null && _node.Attributes["Name"] != null 
                    ? _node.Attributes["Name"].Value : _node.Name;
                return result;
            }
            set
            {
                throw new Exception("Can't change displayname");
            }
        }
    }

    public class ViewModel
    {
        public const string XmlSource =
@"<Root>
  <Names>
    <Name Key=""0"" Name=""Roman""/>
    <Name Key=""1"" Name=""Dmitriy"" />
    <Name Key=""2"" Name=""Alexandr"" />
  </Names>
  <Surnames>
    <Surname Key=""0"" Name=""Mejtes""/>
    <Surname Key=""1"" Name=""Pupkin"" />
    <Surname Key=""2"" />
  </Surnames>
</Root>";

        public ViewModel()
        {
            MakeXmlRoot();
        }

        private void MakeXmlRoot()
        {
            var document = new XmlDocument();
            document.LoadXml(XmlSource);
            RootElements = new ObservableCollection<BaseTreeItem> { new XmlTreeItem(document.ChildNodes[0]) };

        }
        public ObservableCollection<BaseTreeItem> RootElements  { set;  get; }
    }

    <TreeView ItemsSource="{Binding RootElements}">
        <TreeView.ItemContainerStyle>
            <Style TargetType="{x:Type TreeViewItem}">
                <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}"/>
                <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}"/>
            </Style>
        </TreeView.ItemContainerStyle>
        <TreeView.ItemTemplate>
            <HierarchicalDataTemplate ItemsSource="{Binding Children}" >
                <TextBlock Text="{Binding DisplayName}"/>
            </HierarchicalDataTemplate>
        </TreeView.ItemTemplate>
    </TreeView>