title: How to make duplicate indexes a MultiIndex column
body: <p>I have a dataset in which there are two index columns. The first one is a MultiIndex and the second is a normal index, but with lots of duplicate entries. I'd like to join those indexes into a second level MultiIndex.</p>
  <p>i have something like this:</p>
  <pre><code>                         column1|column2|column3|column4|column5|column6|column7
  ---------------------------------------------------------------------
  MultiIndex1|      a      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      a      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      a      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      b      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      b      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      b      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
  </code></pre>
  <p>I'd like my output to look like this:</p>
  <pre><code>                         column1|column2|column3|column4|column5|column6|column7
  ---------------------------------------------------------------------
  MultiIndex1|      a      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |             | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |_____________| 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |      b      | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |             | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
             |             | 1.00 |  2.00 |  3.00 |  4.00 |  5.00 |  6.00 |  7.00
  </code></pre>
  <p>Any help would be immensely appreciated.
  thank you!</p>
  <p><a href="https://i.stack.imgur.com/X7MWT.png" rel="nofollow noreferrer">Dataset head</a></p>
  <p>Sorry, don't have enough reputation to post images.</p>