I'm trying to change the icon of my TreeView in a folder icon. Also when it collapses it needs to have an opened folder icon.

My treeview has databound items in it and the code is:

<TreeView x:Name="TreeViewCategories"  Grid.Row="0" Grid.Column="1" Height="610" HorizontalAlignment="Left"  Margin="29,111,0,0" VerticalAlignment="Top" Width="315" BorderThickness="0" Background="Transparent" >
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate  ItemsSource="{Binding Items}">
            <TextBlock FontSize="20" Text="{Binding Name}" PreviewMouseDown="TextBlock_PreviewMouseDown"/>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
</TreeView>

Also this is how I fill the treeview with items from XML (It's a snipped out of alot of code:

private void LoadHospitalXML()
{
    try
    {
        FileStream fs = new FileStream("ConfigOrgHospital.xml", FileMode.Open, FileAccess.Read);

        var xml = XmlReader.Create(fs);

        rootElement = ConvertHospitalData(xml);

        this.TreeViewCategories.ItemsSource = null;
        List<HospitalWrapper> li = new List<HospitalWrapper>();
        var hosp = rootElement.Items.FirstOrDefault();
        if (hosp != null)
        {
            foreach (var i in hosp.Hospital)
            {
                li.AddIfNotNull(CreateHospList(i));
            }
        }

        this.TreeViewCategories.ItemsSource = li;
    }
    catch (Exception e)
    {
        MessageBox.Show(e.Message);
    }

}

private HospitalWrapper CreateHospList(object obj)
{
    var newItem = new HospitalWrapper();

    newItem.Context = obj;
    //Hospital Names//
    if (obj is HospitalDataHospitalsHospital)
    {
        var hosp = (HospitalDataHospitalsHospital)obj;

        //newItem.Title = "Hospitals";
        newItem.Name = hosp.DefaultName;

        var tmp = new HospitalWrapper();
        tmp.Name = "Sites";
        tmp.IsTitle = true;

        if (hosp.Sites != null)
            foreach (var i in hosp.Sites)
            {
                tmp.Items.AddIfNotNull(CreateHospList(i));
            }
        newItem.Items.Add(tmp);

        tmp = new HospitalWrapper();
        tmp.Name = "Specialties";
        tmp.IsTitle = true;

        if (hosp.Deps != null)
            foreach (var j in hosp.Deps)
            {

                tmp.Items.AddIfNotNull(CreateHospList(j));
            }

        newItem.Items.Add(tmp);
    }
}