Wis. Stat. § 219.02: Securities eligible for investment may be used as collateral.

Wherever, by statute of this state, collateral is required as security for the deposit of public or other funds; or deposits are required to be made with any public official or department; or an investment of capital or surplus, or a reserve or other fund, is required to be maintained consisting of designated securities, notes and bonds insured and debentures issued by the federal housing administrator and obligations of national mortgage associations shall be eligible for such purposes.