public void AddItem()
{
DataItem parent = (DataItem)TreeView.SelectedItem;
if (parent == null)
{
parent = TreeView.Items.OfType <DataItem>().First();
}
for (int i = 0; i < 1; i++)
{
DataItem item = new DataItem("New Item " + i);
item.Parent = parent;
parent.Children.Add(item);
}
VirtualizingItemContainer itemContainer = TreeView.GetItemContainer(parent);
if (itemContainer != null)
{
//Update arrow visiblity
TreeView.DataBindItem(parent, itemContainer);
TreeView.Expand(parent);
}
}