I am trying to write a custom Approval History related list visualforce page but not able to group actions for each step.
There is a ProcessInstanceStep object but currently there is no way to identify records in this object that is completed in a specific step (step1, step2, .. etc). Not sure how salesforce standard Approval History related list shows records for each step grouped by step. Can you please suggest a solution ?

Looks like salesforce needs to include step number field in ProcessInstanceHistory, ProcessInstanceStep and ProcessInstanceWorkItem objects