In the /NET Assembly, you have to use the AllowDrop property as explained here:

• https://www.exontrol.com/sg.jsp?content=support/faq/net/#dragdrop

By default, the OLEDropMode property is exOLEDropNone. The control provides the following options to define the visual effect when drag and drop items:

•  Background(exDragDropBefore), Specifies the visual appearance for the drag and drop cursor before showing the items. This option can be used to apply a background to the dragging items, before painting the items. By default, the control doesn't draw any background for the items being dragged. For instance, use the Background(exDragDropBefore) = SelBackColor property to specify the same background color/skin for items being dragged as they are selected.
•  Background(exDragDropAfter), Specifies the visual appearance for the drag and drop cursor after showing the items. This option can be used to apply a semi-transparent/opaque background to the dragging items, after painting the items. Use this option to apply a transparent/opaque skin, after the items are painted. For instance, using an color or an opaque skin you can show something else when dragging the items.
• Background(exDragDropListTop), Specifies the graphic feedback of the item from the drag and drop cursor if the cursor is in the top half of the row. Use this option to indicate the graphic to be displayed on the item, when the cursor is in the top half row. By default, nothing is displayed.
• Background(exDragDropListBottom), Specifies the graphic feedback of the item from the drag and drop cursor if the cursor is in the bottom half of the row. Use this option to indicate the graphic to be displayed on the item, when the cursor is in the bottom half row. By default, nothing is displayed. Use the HitTestInfoEnum.exHTBottomHalf flag to check whether the user drags the items in the top half or bottom half of the row.
• Background(exDragDropForeColor), Specifies the foreground color for the items being dragged. By default, the foreground color is black. 

All options, excepts the exDragDropForeColor option accept skins. Use the Appearance.Add method to define new skins in the control.

Currently, the ExTree control supports only manual OLE Drag and Drop operation. See the OLEStartDrag and OLEDragDrop events for more details about implementing drag and drop operations into the ExTree control.