Wis. Stat. § 701.1116

A trustee shall allocate to income an amount received as a distribution of income from a trust or an estate in which the trust has an interest other than a purchased interest, and shall allocate to principal an amount received as a distribution of principal from such a trust or estate. If a trustee purchases an interest in a trust that is an investment entity, or a decedent or donor transfers an interest in such a trust to a trustee, s. 701.1115 or 701.1129 applies to a receipt from the trust.