title: Map/Merge Dataframe Values Vertically and Create Additional Index in Multi-index Dataframe
body: <p>I am new to non-horizonal merging and multi-index pandas operations, and have been experiencing trouble solving this problem. I have a multi-index pandas dataframe with 'Region' as the top level index and 'Pet' under that:</p>
  <pre><code>Region:    Region1  Region1  Region2  Region2
  Pet:       Cat      Dog      Cat      Dog
  0          1        8        5        9
  1          4        3        7        1
  </code></pre>
  <p>I am looking to map the following dataframe to create a third index, 'Kind', below 'Pet':</p>
  <p>New dataframe:</p>
  <pre><code>    Pet  Kind
  0   Cat  Tabby
  1   Dog  Weiner
  </code></pre>
  <p>Objective dataframe:</p>
  <pre><code>Region:    Region1  Region1  Region2  Region2
  Pet:       Cat      Dog      Cat      Dog
  Kind:      Tabby    Weiner   Tabby    Weiner
  0          1        8        5        9
  1          4        3        7        1
  </code></pre>
  <p>I have looked into vertical merging with no success. I may also not have the correct language to describe my problem while searching the web. Any help would be deeply appreciated. Thank you!</p>