Go into html mode and paste the following, then close html mode and open it back up. You'll see what I mean if you focus on the area of code I bolded.
<table>
<thead>
<tr>
<th>Event</th>
<th>Pricing</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<h6>Conference & Expo</h6>
</td>
<td>
<table>
<tbody>
<tr>
<td>first data</td>
<td>second data</td>
<td>third data</td>
<td rowspan="2">
<p>some text to fill space</p>
</td>
</tr>
<tr>
<td>first data</td>
<td>second data</td>
<td>third data</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>