20 Pa. C.S. § 2515
A devise or bequest in a will may be made to the trustee of a trust, including any unfunded trust, established in writing by the testator or any other person before, concurrently with or after the execution of the will. Such devise or bequest shall not be invalid because the trust is amendable or revocable, or both, or because the trust was amended after execution of the will. Unless the will provides otherwise, the property so devised or bequeathed shall not be deemed held under a testamentary trust of the testator but shall become and be a part of the principal of the trust to which it is given to be administered and disposed of in accordance with the provisions of the instrument establishing that trust and any amendment thereof. An entire revocation of the trust prior to the testator's death shall invalidate the devise or bequest unless the will directs otherwise.
20 Pa.C.S. § 2515