title: how to unpivot in pandas for 2 level arguments
body: <p>I have a dataframe that looks like the following image:
  <a href="https://i.stack.imgur.com/DT2PO.png" rel="nofollow noreferrer">my df</a></p>
  
  <p>How in pandas unpivot this data, that look like image down?
  <a href="https://i.stack.imgur.com/UNLMQ.png" rel="nofollow noreferrer">finish data</a></p>
  
  <p>I try do it with df.unstack(), but nothing</p>