Add Service part to Service Item

Hi Experts,

I have added a custom button "Add Part" to the component BT116IT_SRVO , when user click on this button I need to add a line item with Item category as Service part.

Component Details :-

BT116IT_SRVO/GenricITEM and It contains Context node BTADMINI . So when user select item number 10 and click's on add part button then it need's to be add lower item in Item tab of service order item list like below

I done this through CRM_ORDER_MAINTAIN but I need BOL program to perform this action ,

The way what I am thinking is this is table contains collection and each row is called entity so how to add entity to collection in event .Please guide me

Thanks & Regards,

Krishna