Not sure what is causing it. Unfortunately, I will be busy next couple of days. If no help has been provided by the time I am able to help, I will look into it more closely.

No problem, I can try to simply "enable" tree collision when the player goes near the border of the map (as trees are there), a simpler solution but less practical for future updates. It should work for now I think

I do have a little time, yet. Maybe, instead of multiple Tree objects along the edges, you could have one object for a row of trees -- two (with a gap) along the top and one along the other 3 edges.