title: Convert dataframe with tuples into dataframe with multiindex
body: <p>I want to convert a dataframe which has tuples in cells into a dataframe with MultiIndex.
  Here is an example of the table code:</p>
  <pre><code>d = {2:[(0,2),(0,4)], 3:[(826.0, 826.0),(4132.0, 4132.0)], 4:[(6019.0, 6019.0),(12037.0, 12037.0)], 6:[(18337.0, 18605.0),(36674.0, 37209.0)]}
  test = pd.DataFrame(d)
  </code></pre>
  <p>This is how the dataframe looks like:</p>
  <pre><code>        2                 3                   4                   6
  0  (0, 2)    (826.0, 826.0)    (6019.0, 6019.0)  (18337.0, 18605.0)
  1  (0, 4)  (4132.0, 4132.0)  (12037.0, 12037.0)  (36674.0, 37209.0)
  </code></pre>
  <p>This is what I want it to look like</p>
  <pre><code>     2       3        4        6
  0 A  0   826.0   6019.0  18337.0
    B  2   826.0   6019.0  18605.0
  1 A  0  4132.0  12037.0  36674.0
    B  4  4132.0  12037.0  37209.0
  </code></pre>
  <p>Thanks for your help!</p>