Betray twenty in Rome? (6,5)
I believe the answer is:
double cross
'betray twenty in rome?' is the definition.
'double cross' can be an answer for 'betray' (doubling cross is a kind of betraying). I'm unsure of the 'twenty in rome?' bit.
'betray twenty in rome?' is the wordplay.
'betray' becomes 'double+' (I've seen this in another clue).
'twenty in rome?' becomes 'cross' (I can't justify this - if you can you should give a lot more credence to this answer).
'double'+'cross'='DOUBLE-CROSS'
Can you help me to learn more?
(Other definitions for double cross that I've seen before include "Betrayal" , "Betray -- XX?" , "Betray while feigning help" , "Deceive supposed ally" , "Defraud" .)