Rails: category and subcategory tree

Question

Hi I am new to rails ... I am trying to make a category and subcategory tree in rails...can you please guide me..

my schema is as follows:

create_table "categories", :force => true do |t|
    t.string  "name",   :null => false
    t.string  "aka",    :null => false
    t.integer "parent"
  end