Ok, well, I think I found the xml:
Basic tech tree (nothing in it): //Stardock Games/Elemental/data/English/CoreTechTree.xml
The basic structure of the generic tech trees: //Stardock Games/Elemental/data/English/CoreTechs.xml
But the real nitty gritty looks like it is supposed to be race specific. However, there are only two racial tech trees currently defined:
//Stardock Games/Elemental/data/English/TechTreeAmarian.xml
//Stardock Games/Elemental/data/English/Techs_Amarian.xml
//Stardock Games/Elemental/data/English/TechTreeTrog.xml
//Stardock Games/Elemental/data/English/Techs_Trog.xml
Plus: //Stardock Games/Elemental/data/English/Techs_Unique.xml