I have added all the units to my mod (I have about 150 units), and made a new tech tree.
At first, I thought I will use two advances to enable some units. This way, Atomic bomb would require only fission, nuke fission and rocketry, ballistic subs fission and submarine warfare, etc.
I am currently implemting my tehc tree in the game. And it doesn't work! If if use several EnableAdvance lines in my units.txt file, the game loads fine, but only one of the avdance is taken into account.