Microsoft Bing is testing a branded side bar explorer bar on the left side for some branded queries. I was able to replicate it in Safari on Mac but not on Chrome yet. Basically if you search for brands, some will show a sidebar that replicates the sitelinks it shows in the search results.
Here are some screenshots where it shows for large brands like Facebook, Twitter, even Google and Bing. It also shows for smaller brands like Search Engine Land and RustyBrick. Click on any of the images to enlarge:
Heck even for Google and Bing:
Here is a GIF Of it in action from German based SEO, Frank Sandtmann:
I am not sure this is needed but it does stand out in a big way. Bing has been busy with testing side bars.
Forum discussion at Twitter.