Magento offers you the ability to create Anchor Categories. Then this is where its subcategories are shown like layered navigation options. For example if you choose to have ‘Electronics’ as the anchor category, then the subcategories will be shown in a layered navigation way like this;
To create an Anchor Category, you take the steps you would as if you were creating a sub category. First, click on ‘Catalog’ on the navigation bar of the backend of your website, then click ‘Manage Categories’. Then on the left hand side where all the categories are listed make sure that you have clicked on ‘Root Category’, then click ‘Add Subcategory’. Enter all the information you need to on this page and then select ‘Display Settings’ from the top menu bar and where it says ‘Is Anchor’, change the answer to ‘Yes’ and this will create your Anchor Category.