Problem with OS Tag

I am developing an installer for Push To Test TestMaker 5.

I have developed 3 packets, one for Linux, one for Windows and one for Mac.
for Linux OS I use os="unix"
for Mac OS I use os="mac"
for Windows I use os="windows"

My problem is that the Unix Pack also appear when I am working in Mac

I know that inside every mac there is an unix, but I want to know if there is any way that the installer shows only mac packages only and not unix package.

I have developed a small example to show you the problem

Thanks
 ;Push To Test Team