The Tree Aerostat is an aerostat that takes 75 hits to pop, and contains 2 ceramic Bloons. It's appearance is a small green blimp covered with tree branches. It is pushed across the screen by 5 green Bloons, that when the aerostat is popped, will continue heading towards the exit, acting as normal green Bloons. It first comes on round 44.
Seems weak, right?
Well, not exactly. The tree branches will whack nearby towers, doing 5 HP damage! Elemental towers take half damage, and flying towers are not affected.