Choose WiselyG 10

There is no trick to successfully reaching the treasure chamber, but you CAN shorten the time it takes by making a backup of your save data before entering the special stage, and reloading the save if/when you fail. This allows you to immediately return to the special stage rather than waiting for the slots to randomly send you back. If you succeed, I don't believe you can achieve the 5 wins by reloading the same data again and again until you've won 5 times, but I didn't test this, so I could be wrong. Feel free to test it out and I'd be happy to credit you with the discovery if it works. I unlocked this legitimately so I can't recommend one method over another with absolute confidence, but my personal recommendation would be to continue reloading until you reach the chamber, and then return to normal play until you are sent to the special stage legitimately again, making a new back up, etc.