Its my first guide then sorry for my bad english.
First Treasure Chest you can get from achievement "Treasure Hunter". If you want to econome your time you can write down: "TREASURE HUNTER IN THE RYE" (without ") in the event box in lobby.

Second Treasure Chest you can get from achievement "Enthusiast". For this achievement you must write down: "fun" (without " again) in the event box in lobby.

Third Treasure Chest you can get from achievement "Competitor". For this achievement you must unlock competitive mode and play first game. Just reach 3 level in game by playing in any match of game browser.

Thank for attention! Good luck in opening Treasure Chests :)