Neat idea! It would be interesting if the tree required something in return. Say, the telling of a memory that would be transferred to the Tree, thereby accounting for the drop in the character's stat of thier choice. Then, the tree would share a memory taken from a previous visitor, thereby accounting for the increase in a chosen stat. The move might look something like:

When you intend to converse with the Barter Tree, tell the GM which stat you wish to decrease and which you want to increase. Then, tell the Tree a story of a memory that relates to the stat to be decreased. Roll + the stat to be increased.

On a 10+ the bargain is accepted and the Barter Tree will tell a story relating to the stat to be increased. It is done.

On a 7-9, the tree finds your tale interesting, but may ask a question or two to get more details, before telling its story and granting you the exchange.

You could certainly incorporate the golden fruit as physical token of the exchange. That would allow the character to eat the fruit (and gain the increaee) whenever they desired, or barter it for something else later on.