<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE Root [
  <!ELEMENT Root ANY>
  <!ELEMENT Node ANY>
  <!ATTLIST Node Id ID #REQUIRED>
  <!ATTLIST Node ParentID CDATA #REQUIRED >
  <!ATTLIST Node Header CDATA #REQUIRED>
]>
<Root>
  
</Root>

<Window x:Class="WpfApplication1.XmlTreeviewDemo"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:jsCtr="clr-namespace:js.WPFbase.Controls;assembly=jsWPFbase"
        xmlns:sys="clr-namespace:System;assembly=mscorlib" 
        Title="XmlTreeviewDemo"  Height="434" Width="408">
    <Window.Resources>
        <XmlDataProvider x:Key="RootData" XPath="/Root"/>

        <HierarchicalDataTemplate DataType="Node" ItemsSource="{Binding}">
            <TextBlock Text="{Binding XPath=@Header}" />
        </HierarchicalDataTemplate>

        <ContextMenu x:Key="GroupContextMenu">
            <MenuItem Header="Neue Hauptgruppe" Command="New"/
            <MenuItem Header="Grupppe anfügen" Command="Open"/>              
        </ContextMenu>
    </Window.Resources>
 <Grid>
        <TreeView Name="trvTreeViewMain" SelectedItemChanged="trvTreeViewMain_SelectedItemChanged">
            <TreeViewItem ItemsSource="{Binding Source={StaticResource RootData}, XPath=*}" Header="Rezeptgruppen" IsExpanded="True" ContextMenu="{StaticResource GroupContextMenu}"/>
        </TreeView>

        </Grid>

</Window>

public class GroupItem : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        private string _header;
        private int _id;
        private int _parentID;

        public GroupItem(string header, int id, int parentID)
        {
            Header = header;
            Id = id;
            ParentID = parentID;
        }

        public string Header
        {   
            get { return _header; }
            set
            {
                _header = value;
                Changed("Header");
            }
        }

        public int Id
        {
            get { return _id; }
            set
            {
                _id = value;
                Changed("Id");
            }
        }

        public int ParentID
        {
            get { return _parentID; }
            set
            {
                _parentID = value;
                Changed("ParentID");
            }
        }


        public override string ToString()
        {
            return Header;
        }

        private void Changed(string propertyName)
        {
            if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class XmlDoc : XmlDocument
    {

        public XmlDocument GetDocument { get { return this; } }

        private XmlElement _rootElement = null;
        private int _treeViewIndex = 0;

        public XmlDoc(string path)
        {
            try
            {

                this.Load(path);

                _rootElement = this.DocumentElement;
            }

            catch (Exception e) { throw e; }

        }

        public void AddElement(XmlElement element, int parentID)
        {
            if (parentID < 1)
            {
                _rootElement.AppendChild(element);
            }
            else
            {
                XmlElement el = this.GetElementById(IdToString(parentID));
                el.AppendChild(element);
            }
        }

        public string IdToString(int id)
        {
            return "_" + id.ToString();
        }

        public int IdToInt(string id)
        {
            return int.Parse(id.Substring(1));
        }

        public int GetTreeViewIndex
        {
            get
            {
                _treeViewIndex++;
                return _treeViewIndex;
            }
        }

    }

    public partial class XmlTreeviewDemo : Window
    {

        private ObservableCollection<GroupItem> _dataCollection;
        private XmlDataProvider _dataProvider = null;
        private XmlDoc _document = null;
        private int _newID = 15;

        public XmlTreeviewDemo()
        {
            CommandBindings.Add(new CommandBinding(ApplicationCommands.New, AddNewGroup));
            CommandBindings.Add(new CommandBinding(ApplicationCommands.Open, AddNewGroup));

            _dataProvider = (XmlDataProvider)trvMain.FindResource("RootData");

            AddData();
            AddDocument();

        }

        private void AddData()
        {

            _dataCollection.Add(new GroupItem("Fleisch", 1, -1));
            _dataCollection.Add(new GroupItem("Rind", 2, 1));
            _dataCollection.Add(new GroupItem("Kalb", 3, 1));
            _dataCollection.Add(new GroupItem("Schwein", 4, 1));
            _dataCollection.Add(new GroupItem("Geflügel", 5, 1));
            _dataCollection.Add(new GroupItem("Huhn", 6, 5));
            _dataCollection.Add(new GroupItem("Beilagen", 7, -1));
            _dataCollection.Add(new GroupItem("Kartoffel", 8, 7));
            _dataCollection.Add(new GroupItem("Teigwaren", 9, 7));
            _dataCollection.Add(new GroupItem("Teigspeisen", 10, 7));
            _dataCollection.Add(new GroupItem("Niocci", 11, 10));
            _dataCollection.Add(new GroupItem("Brust", 12, 6));
            _dataCollection.Add(new GroupItem("Schnitzel", 13, 12));
            _dataCollection.Add(new GroupItem("Geschnetzeltes", 14, 12));

        }


        private void AddDocument()
        {

            _document = new XmlDoc("MyPtah");

            foreach (cit.GroupItem item in _dataCollection)
            {
                if (item.ParentID == -1)
                {
                    _document.AddElement(CreateNewElement(item), -1);
                }
                else
                {
                    _document.AddElement(CreateNewElement(item), item.ParentID);
                }
            }

            _dataProvider.Document = _document.GetDocument;

        }

        private XmlElement CreateNewElement(GroupItem item)
        {

            XmlAttribute atId = _document.CreateAttribute("Id");
            atId.Value = _document.IdToString(item.Id);
            XmlAttribute atPId = _document.CreateAttribute("ParentID");
            atPId.Value = item.ParentID.ToString();
            XmlAttribute atHeader = _document.CreateAttribute("Header");
            atHeader.Value = item.Header;
           
            XmlElement el = _document.CreateElement("Node");
            el.Attributes.Append(atId);
            el.Attributes.Append(atPId);
            el.Attributes.Append(atHeader);

            return el;

        }

        private void AddNewGroup()
        {
            GroupItem item = new GroupItem("Irgendwas", _newID, -1);
            _newID++;
            _document.AddElement(CreateNewElement(item),-1);

            SetElementSelected(item);

        }

        private void AddGroup()
        {

            int parentID = _document.IdToInt(GetSelectedItem().Attributes["Id"].Value);
            GroupItem item = new GroupItem("Irgendwas", _newID, parentID);
            _newID++;

            _document.AddElement(CreateNewElement(item), -parentID);
            //Da hier im TreeView das Element nicht angezeigt wird, den TreeView neu laden
            AddDocument();

            SetElementSelected(item);
        }


        private XmlNode GetSelectedItem()
        {
            try
            {
                return (XmlNode)trvMain.SelectedItem;
            }
            catch { return null; }
        }


        private void SetElementSelected(GroupItem item)
        {
            XmlNode nd = _document.GetElementById(_document.IdToString(item.Id));
            //Hier kommt der Aufruf zu der Function, siehe Link

        }


    }