Line Items with sub-line items – is there easy way to achieve?

Our customer has one issue – he has multiple lineitems fields – this is completely normal and OK. But he needs more lineitems, which have to be UNDER normal lineitem and again another lineitems under THIS sub-line item..

Is there any easy way to do this?

Thank you in advance.

I.E. : —–>

Lineitem 1 —->Lineitem1.1,Lineitem1.2., Lineitem 1.3…….Lineitem 1.15

Lineitem 1.1 —> Lineitem 1.1.1, Lineitem1.1.2…….Lineitem1.1.15