You can drag-and-drop C1TreeViewItems on nodes, in between nodes, or from one tree to another tree when the AllowDragDrop property is set to True.
The following image shows a C1TreeViewItem being dragged from one C1TreeView to another C1TreeView. An arrow or vertical line can be used as a visual cue to show you where the C1TreeViewItem is going to be dropped when either the DragDropArrowMarker or DragDropLineMarker properties are applied.