title: Pandas multilevel columns dataframe
body: <p>I have a df with 48 columns and i want to rename them on two levels as in the dict below:</p>
  <pre><code>{'A': ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
   'B': ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
   'C': ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
   'D': ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']}
  </code></pre>
  <p>i would like to get something like this:
  <a href="https://i.stack.imgur.com/tfNDb.png" rel="nofollow noreferrer">dataframe</a></p>