public class CustomTreeListView : RadTreeListView
{
	protected override AutomationPeer OnCreateAutomationPeer()
	{
		return new CustomTreeListViewAutomationPeer(this);
	}
}

public class CustomTreeListViewAutomationPeer : RadTreeListViewAutomationPeer
{
	public CustomTreeListViewAutomationPeer(RadTreeListView owner) 
		: base(owner)
	{
		var methodInfo = typeof(RadTreeListViewAutomationPeer).GetMethod("GetItemPeers", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);
		methodInfo.Invoke(this, null);
	}

	protected override List<AutomationPeer> GetChildrenCore()
	{
		var frameworkPeer = new FrameworkElementAutomationPeer((FrameworkElement)this.Owner);
		return frameworkPeer.GetChildren();
	}
}

    I found a bug when use MergeCells in grid view and tree list view, I am the license account, my support is out of date,But I still want to feadback the bug to you ， I make a vedio in attachment

When use in radtreelistview , I can not explict set the MergedCellsStyle, maybe MergedCellsStyleSelector also have the bug.I just try MergedCellsStyle.

private void RadTreeListView_Filtering(object sender, Telerik.Windows.Controls.GridView.GridViewFilteringEventArgs e)
{
    var treeListView = sender as RadTreeListView;
    var internalColumns = treeListView.GetType().GetProperty("InternalColumns", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance).GetValue(treeListView);
    internalColumns.GetType().GetProperty("ColumnWidthsCalculationPending", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic).SetValue(internalColumns, true);
}

private void RadTreeListView_Filtered(object sender, Telerik.Windows.Controls.GridView.GridViewFilteredEventArgs e)
{
    Dispatcher.BeginInvoke(new Action(() =>
    {
        var treeListView = sender as RadTreeListView;
        var internalColumns = treeListView.GetType().GetProperty("InternalColumns", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance).GetValue(treeListView);
        internalColumns.GetType().GetProperty("ColumnWidthsCalculationPending", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic).SetValue(internalColumns, false);
    }), System.Windows.Threading.DispatcherPriority.Loaded);
}