Creating sub sections (groups) of layers in QGIS?

I am working on a project regarding Fish species and fishing methods with many layers.

This creates confusion.

I would like to create layer sub sections (groups) like the following:

• 
  

  Fish Species

  
  
  
  
  
  • species 1
  
  
  • species 2
  
  
  • species 3
  
  
  
  


• 
  

  Fishing Methods

  
  
  
  
  • method 1
  
  
  • method 2
  
  
  
  • method 3
  
  
  
  

and so on.

Possibly even a 2nd level sub section (layer group).

I have no idea how to tackle this.

I'm using QGIS 2.4.

To clarify an image of the project is below.

Answer

There is another option: Select multiple layers (using either Shift-click to select a group or Ctrl click to individually add layers to your selection). When you have several selected, right-click and choose "Group Selected". I find this less fiddly than first creating the group and then dragging layers to it (although that is a perfectly valid option).