PonyORM create two sets inside an entity that relates to one entity

Question

i have two item of kota (city in indonesian), and have two kinds (_asal and _tujuan) which translates to 'from' and 'to'. i want this as two Sets that relates to "Daerah" which holds the data for kota.

#this is the sample code

class Daerah(db.Entity):
    id_provinsi = Set(Provinsi)
    kota = Required('RefundPesawat')
    isKota = Required(bool)

class RefundPesawat(db.Entity):
    kota_asal = Set(Daerah)
    kota_tujuan = Set(Daerah)
    tiket_bisnis = Required(int)
    tiket_ekonomi = Required(int)

seems legit as someone who read the "getting started" page of ponyorm

but to my confusion i got this error

pony.orm.core.ERDiagramError: Ambiguous reverse attribute for Daerah.kota. Use the 'reverse' parameter for pointing to right attribute

maybe some of you have any explanation for this