Our Family Tree Builder software doesn't have a Mac version yet.
We've received many requests for this, so producing a Mac version is definitely in our plans. In the meantime, you can wait until we have a Mac version, or continue to grow your tree online.
A tree can be built online on MyHeritage.com, using a Mac. If you have a tree already and it has been published into your own family site on MyHeritage.com, we can, at your request, flip a switch so you'll be able to continue editing your tree online on your Mac, with a browser. Please let me know if you'd like that. You can also import an existing tree into MyHeritage.com via import GEDCOM, and then continue editing it online on the Mac. Let me know if you need assistance with this.