There are two ways:
- make displaying categories without subcategories and use then pagination ... so e.g. only 20 categories will be displayed on the site.
- or using subcategories, etc. If subcategories are used, then you need to load all the categories from database and then create a tree from them. This can be memory demanding but there is no other way. There are different ways to load categories and display them in tree but all the ways are very difficult systems (e.g. tree traversal, etc.)
So displaying categories and using subcategories in tree is nice feature but it is memory demanding
Jan