Wis. Stat. § 846.18: Tardy confirmation of sale.

In all cases where a mortgage foreclosure sale has been made but not confirmed and the purchaser or the purchaser’s successor or assign has taken possession of the land by virtue of said sale, and occupied it for 6 years from and after said sale, the purchaser may apply for and the court may enter an order confirming said foreclosure sale with the same force and effect as if said confirmation was made as otherwise provided by law.