Tandem Circuit Breaker, Stacked style, or Piggyback style.

Piggyback style: 

https://www.sselectricalsupply.com/products/square-d-qot2020-twin-tandem-piggy-back-20a-20a-circuit-breaker-metal-hook-1

Or Stacked style

https://www.sasanelectricals.com/sqdqot20asit.html?gclid=Cj0KCQjwmICoBhDxARIsABXkXlJ_JMWjcivl0Jz6BvwFqXRxb_ud2S2LR2rqf7SEYPHNWpVOU8bXeaIaAjxSEALw_wcB

Normal side-by-side. 

https://www.homedepot.com/s/tandem%20circuit%20breaker%20stacked?NCNI-5