Example nested structure

{ 
  {
    :name => "root_category_1",
    :id => "1",
    :parent_category_id => nil,
    :children => 
      {
        :name => "child_category_1",
        :id => "2",
        :parent_category_id => 1,
        :children => ...
      }
  },
  {
    :name => "root_category_2",
    :id => "3",
    :parent_category_id => nil,
    :children => 
      {
        :name => "child_category_2",
        :id => "4",
        :parent_category_id => 3,
        :children => ...
      }
    }
  }
}