I think at this point we're all well aware that the Tech Tree could do with some improvement. This hopefully will be an passable solution until Firaxis releases a patch.
Information such as Envoys, Embarkment, Improvement yields have been added to the screen. Be forewarned this mod is NOT comprehensive. Some abilities that are unlocked via techs (Tourism boost from Printing, Urban Defenses, etc.) do not currently have icons. Regardless, this mod should hopefully make things clearer.
Extract to your Mods or DLC folders as you prefer. The mod is set to be active by default.
Improved Tech Tree 1.2
Adds more information to the Tech and Civic Trees.