pile.rb

class Hash
  def pile(key, *args)
    if args.count < 2
      self[key] = args[0]
    else
      self[key] ||= {}
      self[key].pile(args.shift, *args)      
    end
  end
end

h = {}
h.pile(:a, :b, :c, 2)
# => {:a=>{:b=>{:c=>2}}}