TransGaming hopes to rejuvenate itself by offering GameTree as a centralized game distribution/management platform for Linux PCs and like systems, including set-top and mobile devices. Basically it's set to be similar to Valve's Steam Content Delivery Platform or the new alternative, Desura. Steam is still coming to Linux with the Source Engine, which will immediately jump to the front, and Desura is also looking at possibly offering a Linux client too of its digital distribution system.
But unlike Steam, which will be native Linux ports and its titles are available for Linux / Mac OS X / Windows all at one price, with GameTree they will still effectively be the Windows builds running atop Cedega and likely with additional fees. TransGaming is offering GameTree for free, but it's hoping to generate revenue via distributing compatible games to Linux users and other devices (this is done via their GameTree TV component).
But in reality, unless TransGaming is able to come up with some compelling offer, you're really just best off buying the Windows game and then running it under Wine, which will not cost you any additional money, or to purchase a CodeWeavers CrossOver license. CrossOver will set you back $39.95, but you're not limited to the number of games / Windows software you can run with that license. CodeWeavers as a company also supports upstream Wine development, compared to Cedega (or previous to that, WineX) using a vastly outdated fork of Wine with no upstream support.