This block is capable of letting the site admin to create a collapsable/expandable menu.

Once you create a number of web pages in your moodle site, you edit the block config, and create the tree using nested bulleted lists. Link the various items to pages by using the ordinary hyperlink tool.

As soon as the block config isa saved, you have your navigable menu.

Note: The pages you add should have the "Allow left and right columns" checkobx enabled to make the menu block to appear.