title: Undo a Git merge that hasn't been pushed yet
body: <p>I accidentally ran <code>git merge some_other_branch</code> on my local master branch. I haven't pushed the changes to origin master. How do I undo the merge?</p>
  <hr />
  <p>After merging, <code>git status</code> says:</p>
  <pre><code># On branch master
  # Your branch is ahead of 'origin/master' by 5 commits.
  </code></pre>
  <p>How do I undo all these commits?</p>