I don't want to give too much away, but there is a special building on the first tab of the build interface, look there. Then keep adding population to it and see what happens. :-)
Hint: Level up your pistol first. Add damage when you level up until you can kill the slow movers in 3 shots and the fast movers in 2. Then play Unlimited > No Way Out. You'll level up quickly and get the bonuses. Good luck! And to the dev: great game -- the last update made this game 10x better. Keep it up!
One of the best games I've played on Kong. Some people are complaining about grammar mistakes, but as a dev you should focus on what's most important: hot keys for units, controls, and assigning to a button (i.e. select a Unit, press Shift+1, then press 1 again to select them). The only gameplay feature I would add is a bonus for higher difficulty. Keep crushing it! :)
 "Mini Healer"){kind=icon}
 "Tank Biathlon"){kind=icon}
 "Questmore"){kind=icon}
 "Turbo Town"){kind=icon}
 "Deterministic Dungeon"){kind=icon}
 "How to kill a zombie"){kind=icon}
 "Clickilization"){kind=icon}
 "Royal Protectors"){kind=icon}
 "Bloons Monkey City"){kind=icon}
 "Spiral Drive"){kind=icon}
 "Royal Warfare"){kind=icon}
 "Kingdom Rush Frontiers"){kind=icon}
 "Toxers"){kind=icon}
 "Micro Olympics"){kind=icon}
 "Infectonator: Hot Chase"){kind=icon}
 "Obliterate Everything 3"){kind=icon}
 "Shop Empire Rampage"){kind=icon}
Good idea!