<PAGE>


                                                         Executed in 6 Parts
                                                         Counterpart No. (   )


                              NATIONAL EQUITY TRUST

                           TOP TEN PORTFOLIO SERIES 28

                            REFERENCE TRUST AGREEMENT


     This Reference Trust Agreement dated February 28, 2001 among Prudential
Securities Incorporated, as Depositor and The Bank of New York, as Trustee, sets
forth certain provisions in full and incorporates other provisions by reference
to the document entitled "National Equity Trust, Trust Indenture and Agreement"
(the "Basic Agreement") dated February 2, 2000. 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.

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

    (i)  Section 3.14  Deferred  Sales Charge shall be amended to add the
         following sentences at the end thereof:


<PAGE>

                                      -2-


         "References to Deferred Sales Charge in this Trust Indenture and
         Agreement shall include any Creation and Development Fee indicated in
         the prospectus for a Trust. The Creation and Development Fee shall be
         payable on each date so designated and in an amount determined as
         specified in the prospectus for a Trust."

                                    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, Top Ten Portfolio Series
28.

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

     C. The publicly traded stocks 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.

     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 March 6, 2001.

     H. The terms "Computation Day" and "Record Date" mean on the tenth day of
June 2001, September 2001, December 2001, and March 2002.

     I. The term "Distribution Date" shall mean on the twenty-fifth day of
June 2001, September 2001, December 2001, and March 2002.

<PAGE>

                                      -3-


     J. The term "Termination Date" shall mean April 4, 2002.

     K. The Trustee's Annual Fee shall be $.90 (per 1,000 Units) for 49,999,999
and below units outstanding, $.84 (per 1,000 Units) on the next 50,000,000
Units, $.78 (per 1,000 Units) on the next 100,000,000 Units, and $.66 (per 1,000
Units) on Units in excess of 200,000,000 Units. 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]

<PAGE>

                                      -4-

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