You're seeing a splitButton control, which needs to have exactly two children:
- a button or toggleButton, and
- a menu.
In this case the splitButton has an image set (the pivot table picture) and a child button (with the label 'PivotTable'). The menu then has two children, the two buttons below called PivotTable and PivotChart.
An xml fragment might look like this:
<splitButton id='split' size='large'>
<button id='splitButton' label='SplitButton' image='M' />
<menu id='splitMenu' >
<button id='splitMenuButton1' label='SplitMenuButton1' />
<button id='splitMenuButton2' label='SplitMenuButton2' />
</menu>
</splitButton>
giving me this in Excel: