Wis. Stat. § 224.02: Banking, defined.

The soliciting, receiving, or accepting of money or its equivalent on deposit as a regular business by any person, partnership, association, or corporation, shall be deemed to be doing a banking business, whether such deposit is made subject to check or is evidenced by a certificate of deposit, a passbook, a note, a receipt, or other writing, provided that nothing herein shall apply to or include money left with an agent, pending investment in real estate or securities for or on account of the agent’s principal.