listAllCategories(categoryId = null)
	if(categoryId != null){
		rootCategory = CategoryModel.find({_id: categoryId})
		rootCategory.children = [];
	}

	categories = find (parent == categoriyId)
	categories.forEach(categorie => {

		knowledges = KnowledgeModel->find({category: categorie._id})
		categorie.knowledges = knowledges;
		categorie.children = listAllCategories(categorie._id);
	});
	return categories;