There’s a product available at hobby stores called Gallery Glass. (Basically it’s a paint on stained glass effect that lasts until you peel it off.)
Not sure how it would work on acrylic, but I did a stained glass window on my shower door, that lasted for 15 years until I got tired of it and scraped it off.
It’s self leveling too - give that a try if you can find it.
Ooooo, be sure to show us the tree when it’s ready. What I can see in the photo is very interesting, with all the cardboard layers. And did you make a light box from an Amazon box and frosted plastic?