Neat little concept maybe would have liked simply no collisions on the trees (or just at the very bass of the stumps) opposed to the awkward way you have to walk past them and the apples just add up. Maybe increase the amount of apples that need to be collected each time and not have a limit but let the player continue to collect apples. A function like, y = a * sqrt(x) + b, where b is the amount for wave 1, a is some sort of multiplier (you could mess around in desmos, https://www.desmos.com/calculator), x is the wave number and y is the number of apples you need. This would just add some more complexity to the game and make it a bit more difficult. Other things you might want to consider for future updates are different maps (like maybe night ex..), some form of NPC that is also collecting apples (where trees they visit can no longer be harvested by the player), and visual cues to say what trees have been harvested (just more visual interactivity in general). Finally if you're looking to make a full release (just my speculation from the comments) maybe consider commissioning a composer to write some custom tracks moving away from the chiptune aesthetic (if you want me to point you in the right direction I'll be happy to help). Overall it's got potential but might need a lot of tweaks to be as good as it can be.