Using a tree to find stuff

Im having trouble figuring out how to use a tree to find stuff, or even if my thought is possible.
Im trying to create a search tree - category, with connection to products.
Something like:
class Category {
    private Integer id;
   private String name;
   private List<Category> children;
Now, from this code I should be able to make a visual tree, something like:
  |-id1, Cat1
  |-id2, Cat2
      |-id3, Cat2_1
      |-id4, Cat2_2
          |-id6, Cat2_2_1
  |-id5, Cat3
Then I have my product:
class Product {
  private Integer id;
  private String name;
  private Category category;
  public Product(String name, Category cat) { &.}
say I have:
List<Product> productList;
productList.add(new Product(prod0, Cat2));
productList.add(new Product(prod1,  Cat2_1));
productList.add(new Product(prod2, Cat2_2));
productList.add(new Product(prod3, Cat2_2_1));
productList.add(new Product("prod4", Cat3));

I need to figure out a way to return a List<Product> when Cat2 is selected that contains:
Cat2, Cat2_1, Cat2_2, Cat2_2_1.
What is the easiest way to do this?
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I guess a map is simpler and quicker.
Think of a HashMap of categories, each being a HashMap of key-child pairs.


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kristian_grAuthor Commented:
Do you have any exaples?
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