procedure TForm1.VSTDragOver(Sender: TBaseVirtualTree;
  Source: TObject; Shift: TShiftState; State: TDragState; Pt: TPoint;
  Mode: TDropMode; var Effect: Integer; var Accept: Boolean);
begin
  if Source=VST then Accept := True;
end;

procedure TForm1.VSTDragDrop(Sender: TBaseVirtualTree;
  Source: TObject; DataObject: IDataObject; Formats: TFormatArray;
  Shift: TShiftState; Pt: TPoint; var Effect: Integer; Mode: TDropMode);
var
  S: string;
  Attachmode: TVTNodeAttachMode;
  Nodes: TNodeArray;
  I: Integer;

//--------------- local function --------------------------------------------

  procedure DetermineEffect;

  // Determine the drop effect to use if the source is a Virtual Treeview.

  begin
    // In the case the source is a Virtual Treeview we know 'move' is the default if dragging within
    // the same tree and copy if dragging to another tree. Set Effect accordingly.
    if Shift = [] then
    begin
      // No modifier key, so use standard action.
      if Source = Sender then
        Effect := DROPEFFECT_MOVE
      else
        Effect := DROPEFFECT_COPY;
    end
    else
    begin
      // A modifier key is pressed, hence use this to determine action.
      if (Shift = [ssAlt]) or (Shift = [ssCtrl, ssAlt]) then
        Effect := DROPEFFECT_LINK
      else
        if Shift = [ssCtrl] then
          Effect := DROPEFFECT_COPY
        else
          Effect := DROPEFFECT_MOVE;
    end;
  end;

  //--------------- end local function ----------------------------------------

begin
  Nodes := nil;

  // Translate the drop position into an node attach mode.
  case Mode of
    dmAbove:
      AttachMode := amInsertBefore;
// dmOnNode:
// AttachMode := amAddChildLast; //<------ hier deaktiviert
    dmBelow:
      AttachMode := amInsertAfter;
  else
    AttachMode := amNowhere;
  end;

  if DataObject = nil then
  begin
    // VCL drag'n drop. Handling this requires detailed knowledge about the sender and its data. This is one reason
    // why it was a bad decision by Borland to implement something own instead using the system's way.
    // In this demo we have two known sources of VCL dd data: Tree2 and LogListBox.
  end
  else
  begin
    // OLE drag'n drop. Perform full processing.

    if Source is TBaseVirtualTree then
    begin
      DetermineEffect;
    end
    else
      if Boolean(Effect and DROPEFFECT_COPY) then
        Effect := DROPEFFECT_COPY
      else
        Effect := DROPEFFECT_MOVE;
    InsertData(Sender as TVirtualStringTree, DataObject, Formats, Effect, AttachMode);
  end;
end;