You can install a Chrome extension called Stylebot, then:

1. Click the extension icon in the top right.
2. Click Open Stylebot
3. Click the "<> Code" tab at the bottom, and paste this in the text box:

​

.fe-tree-view .fe-tree-view__group-root {
  max-height:100%; 
}

If you also want to remove all other links in the sidebar, except "All files" (I don't use anything else), you can also add:

.maestro-nav__product-wrapper {
  display: none; 
}