Nice job! The graphics and audio were nicely done! I like the concept, but the game can be quite repetitive since you just shoot the trees and hit enemies. (Although I didn't get very far, so maybe there's more?)
Also, the timer shows large decimal numbers which can be a bit weird. To fix this, you can do:
timer.text = timer.ToString("0"); (This works with TextMeshPro, but I'm not sure about normal text)
This will only display whole numbers, which can make the UI look a lot cleaner!
I think it would be good if the player could also look and shoot up and down. This way the player isn't too limited on where it should shoot.
Overall, you did a great job! I like how you also implemented an endless mode! I also loved the opening cut scenes!