That's cool to hear you're a returning player!
I agree completely, progression is very much needed otherwise what's the point of playing.
That's an interesting point about "discovering" the monsters in trees. I wonder how random trees having monsters in would change the experience of the game. Also, trees with monsters in occasionally twitch, so that could become the only giveaway that monsters are in the trees instead of the darker, thornier appearance.
Would you be interested in testing future versions / projects?