procedure TForm1.TreeView1DragDrop( Sender, Source : TObject; X, Y : Integer );
var
  AnItem: TTreeNode;
  AttachMode: TNodeAttachMode;
  HT: THitTests;
begin
  if TreeView1.Selected = nil then
     Exit;

  HT := TreeView1.GetHitTestInfoAt( X, Y );
  AnItem := TreeView1.GetNodeAt( X, Y );
  if ( HT - [ htOnItem, htOnIcon, htNowhere, htOnIndent ] <> HT ) then
  begin
    if ( htOnItem in HT ) or
       ( htOnIcon in HT ) then
        AttachMode := naAddChild

    else if htNowhere in HT then
        AttachMode := naAdd
    else if htOnIndent in HT then
        AttachMode := naInsert;

    TreeView1.Selected.MoveTo( AnItem, AttachMode );
  end;
end;