After i show the Categories tree;

I successfully showed he Categories tree;-Thank you nicolas. however my question is how does this apply when there are products in main categories and other products in subcategories.
1. products in parent categories do not show??
2. products in parent categories with no subcategories do not show??

thank you.

It depends on how you configure your module. If you deactivate the link on the main categories, your users won't be able to click on the main categories and thus they won't be able to see the products which are only linked directly to these categories.