title: Git : apply the diff between two branches directly to master
body: <p>I have a branch b1, and another b2 which builds on b1. I can see now that b2 is not dependent on b1, and I'd like to create a PR based on the diff <code>b2 - b1</code> and put that up for merging into master first.</p>
  <p>I can see the diff on github if I set it up to compare with b1 (see image), but have no idea how to extract that as a separate PR.</p>
  <p><a href="https://i.stack.imgur.com/48zks.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/48zks.png" alt="diff summary" /></a></p>
  <p>I guess I need to save the diff to a file and then create a branch from master to apply that to.</p>
  <p>Per the request @LeGEC, this is the result</p>
  <pre><code>* ec82b57a7 (origin/sh/datatree-queries, sh/datatree-queries) tidier
  * ddcb05459 tidier
  * 6ebb2199f tidier
  * 10e3a5e0f clipboard items
  * ff08a1310 wip - UI
  * 0169a4dbe insert entire query ast
  | * 4e8a00c1a (HEAD -&gt; sh/datatree-fx, origin/sh/datatree-fx) revert
  |/  
  o 63d147bc7 Merge remote-tracking branch 'origin/master' into sh/datatree-fx
  </code></pre>