Wis. Stat. § 856.29

If the will of the decedent provides for a testamentary trust, the court shall appoint the trustee upon admission of the will to probate at the same time that letters are granted to the personal representative, unless the court otherwise directs. The trustee so appointed shall continue to be interested in the estate, and beneficiaries in the testamentary trust shall cease to be interested in the estate except under s. 851.21 (3). Letters of trust shall not be required to evidence the authority of a testamentary trustee and a certification of trust under s. 701.1013 shall be sufficient evidence of such authority. This section shall apply to wills admitted to informal probate and letters issued in informal administrations.