public void SetLeftIndentLengthSettings() { var indentLength = TreeViewItemExtension.GetItemIndentLength(AttachedFrameworkElement); var count = AttachedFrameworkElement.FindAscendantCount <TreeViewItem, TreeView>(); var leftIndentLengthDelta = count > 0 ? indentLength * count : 0; _templateSettings.SetValue(TreeViewItemTemplateSettings.ItemIndentThicknessDeltaProperty, new Thickness(leftIndentLengthDelta, 0, 0, 0)); }