title: Stacked bar chart by groups in C3JS
body: <p>How can i have a group within a group for a stacked bar chart?</p>
  
  <pre><code>I have multiple accounts, which have buys and sells. 
  
  I need to display the buys and sells in a stacked bar chart for each account. 
  </code></pre>
  
  <p>I can show just the buys and sell. The tricky bit is showing the buys and sells for each account. any ideas?</p>