<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="200" Width="200">
    <Grid>
        
        <ScrollViewer Margin="0" VerticalAlignment="Stretch">
            
            <ListBox Height="Auto" VerticalAlignment="Stretch">
                
                <TreeView VerticalAlignment="Stretch" Height="Auto">
                    <TreeViewItem Header="Pippo"></TreeViewItem>
                    <TreeViewItem Header="Pippo"></TreeViewItem>
                    <TreeViewItem Header="Pippo"></TreeViewItem>
                    <TreeViewItem Header="Pippo"></TreeViewItem>
                    <TreeViewItem Header="Pippo"></TreeViewItem>
                    <TreeViewItem Header="Pippo">
                        <TreeViewItem Header="Pippo"></TreeViewItem>
                        <TreeViewItem Header="Pippo"></TreeViewItem>
                        <TreeViewItem Header="Pippo">
                            <TreeViewItem Header="Pippo"></TreeViewItem>
                            <TreeViewItem Header="Pippo"></TreeViewItem>
                            <TreeViewItem Header="Pippo">
                                <TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem>
                                <TreeViewItem Header="Pippo">
                                    <TreeViewItem Header="Pippo"></TreeViewItem><TreeViewItem Header="Pippo"></TreeViewItem>
                                </TreeViewItem>
                            </TreeViewItem>
                        </TreeViewItem>
                        <TreeViewItem Header="Pippo"></TreeViewItem>
                    </TreeViewItem>
                </TreeView>
                    
            </ListBox>
            
        </ScrollViewer>
        
    </Grid>
</Window>