public override DragAndDropVisualMode DoDrag(TreeViewItem parentItem, TreeViewItem targetItem, bool perform, DropPosition dropPos)
        {
            var hierarchyTargetItem = targetItem as GameObjectTreeViewItem;

            // Allow client to handle drag
            if (m_CustomDragHandling != null)
            {
                DragAndDropVisualMode dragResult = m_CustomDragHandling(parentItem as GameObjectTreeViewItem, hierarchyTargetItem, dropPos, perform);
                if (dragResult != DragAndDropVisualMode.None)
                {
                    return(dragResult);
                }
            }

            // Scene dragging logic
            DragAndDropVisualMode dragSceneResult = DoDragScenes(parentItem as GameObjectTreeViewItem, hierarchyTargetItem, perform, dropPos);

            if (dragSceneResult != DragAndDropVisualMode.None)
            {
                return(dragSceneResult);
            }

            if (targetItem != null && !IsDropTargetUserModifiable(hierarchyTargetItem, dropPos))
            {
                return(DragAndDropVisualMode.Rejected);
            }

            var option       = HierarchyDropFlags.None;
            var searchActive = !string.IsNullOrEmpty(dataSource.searchString);

            if (searchActive)
            {
                option |= HierarchyDropFlags.SearchActive;
            }
            if (parentItem == null || targetItem == null)
            {
                // Here we are dragging outside any treeview items:

                if (parentForDraggedObjectsOutsideItems != null)
                {
                    // Use specific parent for DragAndDropForwarding
                    return(DragAndDrop.DropOnHierarchyWindow(0, option, parentForDraggedObjectsOutsideItems, perform));
                }
                else
                {
                    // Simulate drag upon the last loaded scene in the hierarchy (adds as last root sibling of the last scene)
                    Scene lastScene = dataSource.GetLastScene();
                    if (!lastScene.IsValid())
                    {
                        return(DragAndDropVisualMode.Rejected);
                    }

                    option |= HierarchyDropFlags.DropUpon;
                    return(DragAndDrop.DropOnHierarchyWindow(lastScene.handle, option, null, perform));
                }
            }

            // Here we are hovering over items

            var draggingUpon = dropPos == TreeViewDragging.DropPosition.Upon;

            if (searchActive && !draggingUpon)
            {
                return(DragAndDropVisualMode.None);
            }

            if (draggingUpon)
            {
                option |= HierarchyDropFlags.DropUpon;
            }
            else
            {
                if (dropPos == TreeViewDragging.DropPosition.Above)
                {
                    option |= HierarchyDropFlags.DropAbove;
                }

                option |= HierarchyDropFlags.DropBetween;
            }

            bool isDroppingBetweenParentAndFirstChild = parentItem != null && targetItem != parentItem && dropPos == DropPosition.Above && parentItem.children[0] == targetItem;

            if (isDroppingBetweenParentAndFirstChild)
            {
                option |= HierarchyDropFlags.DropAfterParent;
            }

            int gameObjectOrSceneInstanceID = GetDropTargetInstanceID(hierarchyTargetItem, dropPos);

            if (gameObjectOrSceneInstanceID == 0)
            {
                return(DragAndDropVisualMode.Rejected);
            }

            if (perform && SubSceneGUI.IsUsingSubScenes() && !IsValidSubSceneDropTarget(gameObjectOrSceneInstanceID, dropPos, DragAndDrop.objectReferences))
            {
                return(DragAndDropVisualMode.Rejected);
            }

            return(DragAndDrop.DropOnHierarchyWindow(gameObjectOrSceneInstanceID, option, null, perform));
        }