class CategoryTree
  attr_reader :id
  attr_reader :name
  attr_reader :children

  def initialize id, name, children=[]
    @id, @name, @children = id, name, children
  end
end

def traverse tree, level = 0
  puts "-- "*level + tree.id.to_s + " " + tree.name
  tree.children.each do |child|
    traverse child, level + 1
  end
end

tree = CategoryTree.new 1, "a", [CategoryTree.new(2, "b", [CategoryTree.new(3333, "g")]), CategoryTree.new(22, "c", [CategoryTree.new(3, "d"),CategoryTree.new(33, "e"),CategoryTree.new(333, "f")])]

traverse tree