First-level TOC should be automatically expanded

Currently, the landing pages for our books have the full table of contents with only the top level pages visible. For example:


There is a content reorganization underway in several books which involves reducing the number of items at the top level of the navigation. Would it be possible to have a setting that expands the first level by default? For example, to show this level of information for each part:


Ideally this would be an option that could be set differently for each book (enabled/disabled).