user_gain = {}

transactions.each do |t|
  # bere persenan user ke 1 yg diatas
  user_gain[user_gain_id_1] = [] if user_gain[user_gain_id_1].blank?
  user_gain[user_gain_id_1] << nilai transaksi * 0.2%

  # bere persenan user ke 2 yg diatas
  # get: user_gain_id_2

  user_gain[user_gain_id_2] = [] if user_gain[user_gain_id_2].blank?
  user_gain[user_gain_id_2] << nilai transaksi
end


{
  30: [10000, 20000, 40000],
  50: []
}