Yes, betray is from betrayen from OFr trair from tradere from trans- plus dare.

"Tradere", "vendere", etc. are 3rd conjugation, while the root "dare" is 1st declension. Note also - "sedeo": I sit; "sedo": I cause to be seated.

In English we have transitive/intransitive pairs like lay/lie and set/sit (cf German legen/liegen and setzen/sitzen).

I wonder if "trans-dare" -> tradere and "venum-dare" -> vendere are examples of a similar pattern?

Do ut des.