Can a tbody be inside another one?

While this may work in practice, it is not legal HTML.

However, you are allowed to have multiple TBODY elements in a single TABLE element, so you could do this:

<table> 
  <tbody class="show"> 
    <tr> 
      <td>...</td> 
      <td>...</td> 
    </tr> 
  </tbody>
  <tbody class="hide"> 
    <tr> 
      <td>...</td> 
      <td>...</td> 
    </tr> 
  </tbody>
  <tbody class="show"> 
    <tr> 
      <td>...</td> 
      <td>...</td> 
    </tr> 
  </tbody>
</table> 

Alternatively, you may be able to nest tables, although I wouldn’t really recommend that.