Back in the day, you could consult the paper manual that came with the game 
See this thread I just made. You can see one of the photos shows a technology tree…
PS: One thing I like about the Technology Tree in AoE2:DE is that you can hover over the scrollbar at the bottom of the screen and use the mouse-wheel to scroll left and right! Ooh, just notice you can push mouse to left and right of screen to do the same. You couldn’t do that in AoE2:HD or before. Makes viewing the tech tree a lot easier and enjoyable!
Two things that would make this scrolling even better, though:
- More granularity in how far the tech tree jumps per mousewheel scroll, when using the hover-over-scrollbar method at bottom. It jumps many pixels currently; very jarring and harder to keep track of your place. Smoother/finer control would be wonderful.
- Actually, make it so you don’t even need to hover over the little scroll bar at the bottom to engage the mousewheel left/right scrolling. There’s no need for this from a user’s perspective. You should be able to have your mouse arrow anywhere on the tech tree to mousewheel scroll left/right.
Is cool you can collapse the left-hand panel, too, to make the Tech Tree be full-screen 