Move selected treeviewitem in wpf

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfApplication1"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <HierarchicalDataTemplate DataType="{x:Type local:TreeViewItemViewModel}" ItemsSource="{Binding Path=Children}" >
            <StackPanel Orientation="Horizontal">
                <TextBlock Text="{Binding Path=Data}"/>
                <Button Content="Inside" Click="button2_Click" />
            </StackPanel>
        </HierarchicalDataTemplate>
    </Window.Resources>
    <Grid>
        <TreeView Height="287" HorizontalAlignment="Left" Margin="12,12,0,0" Name="treeView1" VerticalAlignment="Top" Width="186" />
        <Button Content="Outside" Height="23" HorizontalAlignment="Left" Margin="204,41,0,0" Name="button2" VerticalAlignment="Top" Width="75" Click="button2_Click" />
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Collections.ObjectModel;
using System.ComponentModel;
namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        ObservableCollection<TreeViewItemViewModel> nodes;
        protected override void OnActivated(EventArgs e)
        {
            nodes = new ObservableCollection<TreeViewItemViewModel>();
            nodes.Add(new TreeViewItemViewModel("1"));
            nodes.Add(new TreeViewItemViewModel("2"));
            nodes.Add(new TreeViewItemViewModel("3"));
            TreeViewItemViewModel viewModel = new TreeViewItemViewModel("4");
            viewModel.Parent = nodes[0];
            nodes[0].Children.Add(viewModel);
            treeView1.ItemsSource = nodes;
            base.OnActivated(e);
        }
        
        private void button2_Click(object sender, RoutedEventArgs e)
        {
            TreeViewItemViewModel viewModel = nodes[0].Children[0];
            nodes[0].Children.Remove(viewModel);
            viewModel.Parent = nodes[1];
            nodes[1].IsExpanded = true;
            nodes[1].Children.Add(viewModel);
            viewModel.IsExpanded = true;
            viewModel.IsSelected = true;
        }
    }
    public class TreeViewItemViewModel : INotifyPropertyChanged
    {
        public ObservableCollection<TreeViewItemViewModel> Children { get; private set; }
        private bool _isExpanded;
        public bool IsExpanded
        {
            get { return _isExpanded; }
            set
            {
                if (_isExpanded != value)
                {
                    _isExpanded = value;
                    if (Parent != null)
                    {
                        Parent.IsExpanded = true;
                    }
                    OnPropertyChanged("IsExpanded");
                }
            }
        }
        private bool _isSelected;
        public bool IsSelected
        {
            get { return _isSelected; }
            set
            {
                if (_isSelected != value)
                {
                    _isSelected = value;
                    OnPropertyChanged("IsSelected");
                }
            }
        }
        public TreeViewItemViewModel Parent { get; set; }
        public TreeViewItemViewModel(string data)
        {
            Data = data;
            Children = new ObservableCollection<TreeViewItemViewModel>();
        }
        public string Data { get; set; }
        public event PropertyChangedEventHandler PropertyChanged;
        protected virtual void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}