Bulk insert into table with identity row

hi,

I want to insert bulk data into a new table with identity row like

1) 1 to 1,000 records under identity row A1

2) 1,001 to 2,000 records under identity row A2

3) 2,001 to 3,000 records under identity row A3

10) 9,001 to 10,000 records under identity row A10

from 10,001 to 11,000 records under B1

11,001 to 12,000 records under B2

12,001 to 13,000 records under B3

19,001 to 20,000 records under B10

again new index 20,001 to 21,000 records under C1

Please share your ideas on the above