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                                                              EX-4.b


                                                             Executed in 6 Parts
                                                           Counterpart No. (   )


                              NATIONAL EQUITY TRUST

                          LOW FIVE PORTFOLIO SERIES 216

                            REFERENCE TRUST AGREEMENT

               This Reference Trust Agreement dated April 19, 2000 among
Prudential Securities Incorporated, as Depositor and The Chase Manhattan Bank,
as Trustee, sets forth certain provisions in full and incorporates other
provisions by reference to the document entitled "National Equity Trust Low Five
Portfolio Series, Trust Indenture and Agreement" (the "Basic Agreement") dated
April 25, 1995. Such provisions as are set forth in full herein and such
provisions as are incorporated by reference constitute a single instrument (the
"Indenture").

                                WITNESSETH THAT:
                                ---------------


               In consideration of the premises and of the mutual agreements
herein contained, the Depositor and the Trustee agree as follows:

                                     Part I.

                     STANDARD TERMS AND CONDITIONS OF TRUST

               Subject to the provisions of Part II hereof, all the provisions
contained in the Basic Agreement are herein incorporated by reference in their
entirety and shall be deemed to be a part of this instrument as fully and to the
same extent as though said provisions had been set forth in full in this
instrument except that the Basic Agreement is hereby amended in the following
manner:

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A.      Article I, entitled "Definitions", paragraph 22, shall be amended as
        follows:

        "Trustee shall mean The Chase Manhattan Bank
        or any successor trustee appointed as
        hereinafter provided."

B.      Article II, entitled "Deposit of Securities; Acceptance of Trust", shall
        be amended as follows:

        The second sentence of Section 2.03 Issue of Units shall be amended by
        deleting the words "on any day on which the Depositor is the only Unit
        Holder."

C.      Article III, entitled "Administration of Trust", shall be amended as
        follows:

        (i)    Section 3.01 Initial Costs shall be amended to substitute the
               following language:

               Section 3.01. Initial Cost The costs of organizing the Trust and
               sale of the Trust Units shall, to the extent of the expenses
               reimbursable to the Depositor as provided below, be borne by the
               Unit Holders, provided, however, that, to the extent all of such
               costs are not borne by Unit Holders, the amount of such costs not
               borne by Unit Holders shall be borne by the Depositor and,
               provided further, however, that the liability on the part of the
               Depositor under this section shall not include any fees or other
               expenses incurred in connection with the administration of the
               Trust subsequent to the deposit referred to in Section 2.01. Upon
               notification from the Depositor that the primary offering period
               is concluded, the Trustee shall withdraw from the Account or
               Accounts specified in the Prospectus or, if no Account is therein
               specified, from the Principal Account, and pay to the Depositor
               the Depositor's reimbursable expenses of organizing the Trust and
               sale of the Trust Units in an amount certified to the Trustee by
               the Depositor. If the balance of the Principal Account is
               insufficient to make such withdrawal, the Trustee shall, as
               directed by the Depositor, sell Securities identified by the
               Depositor, or distribute to the Depositor Securities

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               having a value, as determined under Section 4.01 as of the date
               of distribution, sufficient for such reimbursement. The
               reimbursement provided for in this section shall be for the
               account of the Unitholders of record at the conclusion of the
               primary offering period and shall not be reflected in the
               computation of the Unit Value prior thereto. As used herein, the
               Depositor's reimbursable expenses of organizing the Trust and
               sale of the Trust Units shall include the cost of the initial
               preparation and typesetting of the registration statement,
               prospectuses (including preliminary prospectuses), the indenture,
               and other documents relating to the Trust, SEC and state blue sky
               registration fees, the cost of the initial valuation of the
               portfolio and audit of the Trust, the initial fees and expenses
               of the Trustee, and legal and other out-of-pocket expenses
               related thereto, but not including the expenses incurred in the
               printing of preliminary prospectuses and prospectuses, expenses
               incurred in the preparation and printing of brochures and other
               advertising materials and any other selling expenses. Any cash
               which the Depositor has identified as to be used for
               reimbursement of expenses pursuant to this Section shall be
               reserved by the Trustee for such purpose and shall not be subject
               to distribution or, unless the Depositor otherwise directs, used
               for payment of redemptions in excess of the per-Unit amount
               allocable to Units tendered for redemption. As directed by the
               Depositor, the Trustee will advance funds to the Trust in an
               amount necessary to reimburse the Depositor pursuant to this
               Section and shall recover such advance from the sale or sales of
               Securities at such time as the Depositor shall direct, but in no
               event later than the termination of the Trust. Repayment of any
               such advance shall be secured by a lien on the assets of the
               Trust prior to the interest of the Unit Holders as provided in
               Section 6.04.

        (ii)   The third paragraph of Section 3.05 Distribution shall be amended
               to add the following sentence at the end thereof:

               "The Trustee shall make a special distribution of the cash
               balance in the Income and Principal accounts available for such
               distribution to Unit Holders of record on such dates as the
               Depositor shall direct."

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        (iii)  The second to the last paragraph of Section 3.08 Sale of
               Securities shall be amended to replace the word "equal" with the
               following phrase: "be sufficient to pay."

D.      Reference to United States Trust Company of New York in its capacity as
        Trustee is replaced by the Chase Manhattan Bank throughout the Basic
        Agreement.

E.      Section 6.05 shall be amended to delete the clause "if the Depositor
        shall determine in good faith that there has oc- curred either (1) a
        material deterioration in the creditwor- thiness of the Trustee or (2)
        one or more negligent acts on the part of the Trustee having a
        materially adverse effect, either singly or in the aggregate, on the
        Trust or on one or more Trusts, such that the replacement of the Trustee
        is in the best interest of the Unit Holders" and insert in place thereof
        "upon the determination of the Depositor to remove the Trustee for any
        reason, either with or without cause, including but not limited to a
        determination by the Deposi- tor that the Trustee has materially failed
        to perform its duties under the Indenture and the interest of Unit
        Holders has been substantially impaired as a result".

                                    Part II.

                      SPECIAL TERMS AND CONDITIONS OF TRUST

               The following special terms and conditions are hereby agreed to:

               A.     The Trust is denominated National Equity Trust, Low Five
                      Portfolio Series 216.

               B.     The Units of the Trust shall be subject to a deferred
                      sales charge.

               C.     The contracts for the purchase of common stock listed in
                      Schedule A hereto are those which, subject to the terms of
                      this Indenture, have been or are to be deposited in Trust
                      under this Indenture as of the date hereof.

               D.     The term "Depositor" shall mean Prudential Securities
                      Incorporated.

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               E.     The aggregate number of Units referred to in Sections 2.03
                      and 9.01 of the Basic Agreement is 125,000 as of the date
                      hereof.

               F.     A Unit of the Trust is hereby declared initially equal to
                      1/125,000th of the Trust.

               G.     The term "First Settlement Date" shall mean April 26,
                      2000.

               H.     The terms "Computation Day" and "Record Date" shall mean
                      quarterly on the tenth day of June, September, December,
                      and March commencing June 10, 2000.

               I.     The term "Distribution Date" shall mean quarterly on the
                      twenty-fifth day of June, September, December, and March
                      commencing June 25, 2000 or as soon thereafter as
                      possible.

               J.     The term "Termination Date" shall mean April 24, 2002.

               K.     The Trustee's Annual Fee shall be $.95 (per 1,000 Units)
                      for 100,000,000 and above units outstanding; $1.01
                      (per 1,000 Units) for 50,000,000 - 99,999,999 units
                      outstanding; $1.05 (per 1,000 Units) for 49,999,999
                      and below units outstanding. In calculating the
                      Trustee's annual fee, the fee applicable to the
                      number of units outstanding shall apply to all units
                      outstanding.

               L.     The Depositor's Portfolio supervisory service fee shall be
                      $.25 per 1,000 Units.

               [Signatures and acknowledgments on separate pages]


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               The Schedule of Portfolio Securities in Part A of the prospectus
               included in this Registration Statement for National Equity
               Trust, Low Five Portfolio Series 216 is hereby incorporated by
               reference herein as Schedule A hereto.