WPF treeview with HierarchicalDataTemplate shows only 1 item - wpf

Question

I am trying to bind to a WPF treeview but I am getting unexpected results. I bind to my viewmodel which appears to work as I get a single item but it does not allow me to expand to child items. I cant see what I'm doing wrong. Does anyone have any ideas?
I have the following model
public class Folder
{
public string Name { get; set; }
public IEnumerable<Folder> Subfolders { get; set; }
}
I have the following view model
public class Vm : INotifyPropertyChanged
{
private IEnumerable<Folder> _items;
public Vm()
{
var x = new List<Folder>();
x.Add(new Folder()
{
Name = "Item1",
Subfolders = new List<Folder>()
{
new Folder()
{
Name = "SubItem1", Subfolders = new List<Folder>()
{
new Folder() { Name = "SubItem2", Subfolders = new List<Folder>()}
}
}
}
});
Items = x;
}
public IEnumerable<Folder> Items
{
get => _items;
set
{
_items = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
My Xaml looks like
<Window x:Class="WpfApp5.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:WpfApp5"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Grid>
<TreeView Height="450" Width="800" ItemsSource="{Binding Path=Items}">
<TreeView.Resources>
<HierarchicalDataTemplate DataType="{x:Type local:Folder}" >
<TextBlock Margin="5,0,0,0" FontWeight="Bold" Text="{Binding Name}"/>
</HierarchicalDataTemplate>
</TreeView.Resources>
</TreeView>
</Grid>
</Window>

Answer 1

Its ok I found it. I needed to add a Items source value to the HierarchicalDataTemplate of Subitems