internal IEnumerable GetChildren(object item)
 {
     if (_childrenPropertyReader == null)
     {
         _childrenPropertyReader = new ItemsControlItemPropertyReader <IEnumerable>(this, VirtualTreeViewItem.ItemsSourceProperty, allowSourceProperties: OptimizeItemBindings);
     }
     return(_childrenPropertyReader.Get(item));
 }
 internal bool IsExpanded(object item)
 {
     if (_isExpandedPropertyReader == null)
     {
         _isExpandedPropertyReader = new ItemsControlItemPropertyReader <bool>(this, VirtualTreeViewItem.IsExpandedProperty, allowSourceProperties: OptimizeItemBindings);
     }
     return(_isExpandedPropertyReader.Get(item));
 }