Group ListView Command Set extension buttons under dropdown?

Following the walkthrough at 

https://docs.microsoft.com/en-us/sharepoint/dev/spfx/extensions/get-started/building-simple-cmdset-with-dialog-api#debugging-your-listview-command-set-using-gulp-serve-and-query-string-parameters

how can I group "Command 1" and "Command 2" under a parent button that functions as dropdown to show these two options?

This is similar but targets a different location: 

https://docs.microsoft.com/en-us/sharepoint/dev/solution-guidance/modern-experience-customizations-customize-lists-and-libraries#user-custom-actions

If there's a way to adapt this to ClientSideExtension.ListViewCommandSet.CommandBar , I am not seeing it.