Bryce K. Nielsen
It's pretty explicit in the rulebook:
This optional rule is for players who wish to access high level Class, Shop
Item, and Overlord cards outside of a campaign setting. When using this
option, all players must agree upon a power level (listed below) after
choosing a quest. For rules on spending experience points, see “Spend
Experience Points” on page 20.
Basic Level: Follow normal setup.
Advanced Level: Each hero receives 3 experience points worth of Class
cards and 150 gold worth of Act I Shop Item cards (of their choice—
heroes may share gold). The overlord receives 4 experience points worth
of Overlord cards.
Expert Level: Each hero receives 6 experience points worth of Class cards
and 250 gold worth of Act I or Act II Shop Item cards (of their choice—
heroes may share gold). The overlord receives 8 experience points worth
of Overlord cards. The overlord uses his Act II Monster and Lieutenant
pg 19 of Descent 2nd Edition Rulebook
So if you are playing Basic or Advanced, you only use Act I treasure cards. If you are playing Expert, you use Act II.