With the Lessons Tool you can now enable subpage navigation in the left-hand tool menu. Doing so will create a collapsible menu for your Lessons modules. 

To enable subpage navigation:

• Access your course
• Select the Site Info tool
• Select Manage Tools
• Check the box to Enable Lessons subpage navigation in the right tool menu
  • You may need to collapse the General menu to view it
• Scroll to the bottom of the screen and select Continue
• You can now collapse (or not) the Lessons menu in the left tool bar

The video (1:00) below demonstrates how to Enable Subpage Navigation for the Lessons Tool