A transfer of property by deed of trust wherein the settlor reserved to himself, or to himself and others not beneficiaries, powers of revocation, alteration or amendment, upon the exercise of which the property might revest in him, shall, upon the death of the settlor, be taxable to the extent of the value of the property subject to such powers and with respect to which such powers remained unexercised. The word “property”, as used in this section, shall not include the proceeds of any policy of life, accident or health insurance, payable to a named beneficiary or beneficiaries, or the executors of the will or the administrators of the estate of the insured, nor the proceeds of any policy of war risk insurance, United States government life insurance or national service life insurance.