Requirements:
Bankroll should exceed 590,050 credits.

Player should have reached level 45.

Method:
Buy the pyramid stack from the shop.
Make sure the pyramid stack is equipped.
Start up a single player Ring Game.
Keep playing, and rebuying, untill the pyramid stack is filled.
Once the pyramid stack is filled the achievement pops up.

Important notes:
In single player mode it is not possible to lose credits from your bankroll. Basically the player can do infinite rebuys in a single player Ring Game, This allows for the player to adopt an aggressive betting strategy.

The pyramid stack unlocks once the player reaches level 45.

The pyramid stack can be bought for 580,050 credits. Keep an eye on the weekly promotion boost. If the pyramid stack is in the weekly promotion this will give you a considerable (50%) discount.

Recommendations:
I would suggest to chase this achievement AFTER getting the "A Cool Million"-achievement.