That's what social progress is supposed to be for. Races get unique SP options sprinkled amongst the shared ones. Playing too much with the Zenith to say what they are.
Rather than unique techs, every race could have a free HISTORY tech that explains some of their remembered history and their initial bonuses, in the vein of GalCiv 2.
If we want to go ahead with "making the races distinct through the tech tree", an extra line of techs representing recovered knowledge would be my suggestion, just as expansion content.