(1) An insurer may invest any of its funds in bonds  notes  or other evidences of indebtedness which are secured by first mortgages or deeds of trust upon improved real property located in the United States or Canada or which are secured by first mortgages or deeds of trust upon leasehold estates having an unexpired term of not less than 40 years (inclusive of the term or terms which may be provided by enforceable options of renewal) in improved real property located in the United States or Canada