WPF-Demo/WpfSample/MainWindow.xaml

<Window x:Class="WpfSample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfSample"
        xmlns:vm="clr-namespace:WpfSample.ViewModels"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800"
        BorderThickness="0" Background="Coral">

    <Grid>

        <Grid.RowDefinitions>
            <RowDefinition Height="36"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <StackPanel Grid.Row="0" Orientation="Horizontal">
            <Button Command="{Binding AddItemCommand}" Content="Add"/>
            <TextBlock x:Name="tb1" local:PropADemo.Text="Hello World"/>
            <TextBlock x:Name="tb2" local:PropADemo.Text="Greeting"/>
        </StackPanel>

        <TreeView Grid.Row="1" ItemsSource="{Binding Groups}">
            <TreeView.Resources>
                <HierarchicalDataTemplate DataType="{x:Type vm:DemoGroupViewModel}" ItemsSource="{Binding Items}">
                    <Border Background="Coral">
                        <TextBlock Text="{Binding Message}"/>
                    </Border>
                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate DataType="{x:Type vm:DemoItemViewModel}">
                    <Border Background="#669999">
                        <TextBlock Text="{Binding Message}"/>
                    </Border>
                </HierarchicalDataTemplate>
            </TreeView.Resources>

            <TreeView.ItemContainerStyle>
                <Style TargetType="TreeViewItem">
                    <Setter Property="AllowDrop" Value="True"/>
                    <EventSetter Event="MouseMove" Handler="TreeViewItem_MouseMove"/>
                    <EventSetter Event="DragEnter" Handler="TreeViewItem_DragEnter"/>
                    <EventSetter Event="DragOver" Handler="TreeViewItem_DragOver"/>
                    <EventSetter Event="DragLeave" Handler="TreeViewItem_DragLeave"/>
                    <EventSetter Event="Drop" Handler="TreeViewItem_Drop"/>
                </Style>
            </TreeView.ItemContainerStyle>

        </TreeView>

    </Grid>
</Window>