I think the double jump height should be increased a bit. Maybe I'm just terrible, but I couldn't get over the first tree on the first level because the double jump height was like half the normal jump height.
The game was tested, the double jump is ok. I don't think is a bug or something, I think you just didn't get the mechanic still =D Try it again and again, you'll get it. Hint: Wait a little bit after the second jump. Good luck!
