Supply with Service.. how to execute

Dear All
Our company is dealing with electrical projects. Trading and service.

Recently we got one order from our customer for supply of some material and for that material installation also and they are treating this order as work contract and given the order also like that as service order

now my doubt is in billing how we have to treat the same

material HSN code 8597100.
service HSN code 998732

customer required only one bill, one HSN code

value Rs. 100000/-


I request you people to give me your valuable suggestions