I love the tree facts!
While moving left or right the inputs for moving up or down get ignored. It would feel more responsive, if the duck moved into whichever direction was pressed last.
Level two has an enemy that moves across the wall, into the void.
It would be nice, if I could close the tree facts by pressing space instead of having to move my hands off the keyboard.
The hit detection feels unfair. E.g. in level 3 the enemy near the flag is far enough from the wall that it should be possible to squeeze through, but the enemy kills me without actually touching me.
The walls have a similar issue. It's frustrating to collide with the air above a wall, when trying to walk around a corner.
The art style of the sprites is inconsistent.
Nice music!