No, the right syntax would be
C:\MyPix\*
It excludes all files in C:\MyPix, including all subfolders.
It is not possible to exclude only the files in C:\MyPix and not the files in its subfolders.
If you use C:\MyPix* - it will work too, but it will also exclude files like C:\MyPixListing.txt, also files in C:\MyPix2 or C:\MyPixAnything folders, etc.