title: How do I find all heads that point to the same treeish
body: <p>Let's say, for example, that I've got branches master, foo, and bar.</p>
  
  <pre><code>master
    \--foo
        |
       bar
  </code></pre>
  
  <p>foo and bar are the same thing. Imagine some work was committed on foo, then the user did <code>git checkout -b bar</code> but never did anything to bar. So, they both point to the same treeish. </p>
  
  <p>Now, lets say time passes and I've forgotten what the name of that other branch was that was the same as foo, or maybe I just want to clean up my branches. </p>
  
  <p><strong>What command do I need to execute when on the foo branch, to see all the other branches that point to the same treeish (in this case just bar)?</strong></p>
  
  <p>How / why is this useful? Well, since pull requests on Github are branches that can be tracked, I can look at an old branch I have sitting around, run this command, and have it show me <code>origin/pr/42</code> and now I have the id of the old pull request (42) to go look at it on Github.</p>