That any tribal land that may be sold pursuant to this Act may, with the approval of the Secretary of the Interior, be encumbered by a mortgage or deed of trust and shall be subject to foreclosure or sale pursuant to the terms of such a mortgage or deed of trust in accordance with the laws of the State of Washington. The United States shall be an indispensable party to any such proceeding with the right of removal of the clause to the United States district court for the district in which the land is located, following the procedure in section
1446 of title
28: Provided, That the United States shall have the right to appeal from any order of remand in the case.