IF branches located in different state then separate registration is required under each state. But in a single state all are added as additional places of business.
Also registration rules as per GST law is given below.(Read point1 for ur clarification)
(1) Every person who is liable to be registered under Schedule V of this Act shall
apply for registration in every such State in which he is so liable within thirty
days from the date on which he becomes liable to registration, in such manner
and subject to such conditions as may be prescribed:
PROVIDED that a casual taxable person or a non-resident taxable person shall
apply for registration at least five days prior to the commencement of business.
(2) Notwithstanding anything contained in sub-section (1), a person having multiple
business verticals in a State may obtain a separate registration for each business
vertical, subject to such conditions as may be prescribed.
(3) A person, though not liable to be registered under Schedule V, may get himself
registered voluntarily, and all provisions of this Act, as are applicable to a
registered taxable person, shall apply to such person.
(4) Every person shall have a Permanent Account Number issued under the Income
Tax Act, 1961 (43 of 1961) in order to be eligible for grant of registration under
sub-section (1), (2) or (3):
PROVIDED that a person required to deduct tax under section 46 shall have, in
lieu of a Permanent Account Number, a Tax Deduction and Collection Account
Number (TAN) issued under the said Act in order to be eligible for grant of
registration.
(5) Notwithstanding anything contained in sub-section (4), a non-resident taxable
person may be granted registration under sub-section (1) on the basis of any
other document as may be prescribed.
(6) Where a person who is liable to be registered under this Act fails to obtain
registration, the proper officer may, without prejudice to any action that is, or
may be taken under this Act, or under any other law for the time being in force,
proceed to register such person in the manner as may be prescribed.
(7) Notwithstanding anything contained in sub-section (1),
(a) any specialized agency of the United Nations Organization or any Multilateral
Financial Institution and Organization notified under the United Nations
(Privileges and Immunities) Act, 1947 (46 of 1947), Consulate or Embassy of
foreign countries shall be granted a Unique Identity Number; and
(b) any other person or class of persons, as may be notified by the Commissioner,
shall obtain a Unique Identity Number,
in the manner prescribed, for the purpose(s) notified, including refund of taxes on
the notified supplies of goods and/or services received by them.
(8) The registration or the Unique Identity Number, shall be granted or, as the case
may be, rejected after due verification in the manner and within such period as
may be prescribelow.
(9) A certificate of registration shall be issued in the prescribed form, with effective
date as may be prescribed.
(10) A registration or an Unique Identity Number shall be deemed to have been
granted after the period prescribed under sub-section (8), if no deficiency has
been communicated to the applicant by the proper officer within that period.
(11) Notwithstanding anything contained in sub-section (8), any rejection of
application for registration or the Unique Identity Number under the CGST Act /
SGST Act shall be deemed to be a rejection of application for registration under
the SGST Act / CGST Act.
(12) The grant of registration or the Unique Identity Number under the CGST
Act / SGST Act shall be deemed to be a grant of registration or the Unique
Identity Number under the SGST/CGST Act provided that the application for
registration or the Unique Identity Number has not been rejected under
SGST/CGST Act within the time specified in sub-section (8).
(13) The Central or a State Government may, on the recommendation of the
Council, by notification, specify the category of persons who may be exempted
from obtaining registration under this Act