How to make a secondary x-axis on column graph

Hi, I need to capture 2 catagories on the x-axis of the chart, one for cohort and one for month. Each cohort will have Jan - July months, there there will be 2 groups on the x-axis. For example, here is my sheet:

and so far my graph looks like this:

The months are correct but I need them grouped with a second axis for cohort ST 5E10 DE and PD-1 5E10 DE.

Can smartsheet do this?