I was researching Alliances to get 'Research Alliance' but, when I got there, the research alliance was not selectable.  Research Alliance is one of the 'focus' techs, and I believe that it is the bottom of the three alliances.

When I was ready to research that 'focus' item, I discovered that the tech item immediately below it had been previously selected and was covering up the Research Alliance tech.  I could barely see the outline of the bottom tech but could not select it.

I believe that the tech tree needs more vertical spacing so the techs don't overlap.