How to simply add a column level to a pandas dataframe
<p>let say I have a dataframe that looks like this:</p>

<pre><code>df = pd.DataFrame(index=list('abcde'), data={'A': range(5), 'B': range(5)})
 df
Out[92]: 
   A  B
a  0  0
b  1  1
c  2  2
d  3  3
e  4  4
</code></pre>

<p>Asumming that this dataframe already exist, how can I simply add a level 'C' to the column index so I get this:</p>

<pre><code> df
Out[92]: 
   A  B
   C  C
a  0  0
b  1  1
c  2  2
d  3  3
e  4  4
</code></pre>

<p>I saw SO anwser like this <a href="https://stackoverflow.com/questions/15989281/python-pandas-how-to-combine-two-dataframes-into-one-with-hierarchical-column-i">python/pandas: how to combine two dataframes into one with hierarchical column index?</a> but this concat different dataframe instead of adding a column level to an already existing dataframe.</p>

<p>-</p>