ExpandableListView elv = (ExpandableListView)findViewById(R.id.expandableListView_categories);
ArrayList<Category> categories3 = new ArrayList<Category>();
categories3.add(new Category("__cat1"));
categories3.add(new Category("__cat2"));
categories3.add(new Category("__cat3"));
categories3.add(new Category("__cat4"));
ArrayList<Category> categories2 = new ArrayList<Category>();
categories2.add(new Category("_cat1"));
categories2.add(new Category("_cat2"));
categories2.add(new Category("_cat3", categories3));
categories2.add(new Category("_cat4"));
ArrayList<Category> categories = new ArrayList<Category>();
categories.add(new Category("cat1"));
categories.add(new Category("cat2", categories2));
categories.add(new Category("cat3"));
categories.add(new Category("cat4"));
CatAdapter adapter = new CatAdapter(this, categories);
elv.setAdapter(adapter);