The Mean Tree is a special agent that costs 60 monkey money. It throws leaves rapidly that pops 2 layers of bloons and pierces through 2 bloons. It can also do 20 damage to MOAB Class Bloons.
"What happens when a tree gets mad? It throws leaves rapidly that pops 2 layers of bloons and pierces through 2 bloons! As an extra popping bonus, it does 20 damage to MOAB Class Bloons! There's no tree meaner than this one!"
It becomes pro when you use it 50 times.
"Pro Mean Tree unlocked! Squirrels! One squirrel comes out of the tree hole every round and throws cocunuts at bloons! Cocunuts are big or small. Big cocunuts pop 2 layers of bloons and 2 pierces just like the tree! Squirrels will last 200 seconds so get them quickly! The next Mean Tree you place will have this upgrade."
Can't make a picture that's good enough.