title: Dropdown list of buttons
body: <p>First I want to mention that I am a beginner in android.</p>
  <p>Basically I am trying to implement the Microsoft's calculator in android.For now I am implementing only the UI.
  Is it possible to make a dropdown list of buttons?</p>
  <p><a href="https://i.stack.imgur.com/sIXE5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sIXE5.png" alt="enter image description here" /></a></p>
  <p>Like in this picture when you select <code>Bitwise</code> a list of buttons appears.Also is it possible <code>Bitwise</code> also to be a button and if not to act like one?</p>