Organization Security in Security Profile

Hi,

My customer has a requirement to setup a Responsibility which has access to Organizations say X and Y and all child Organizations under X and Y. Normally until now it has always only been Organization X and Child Organizations under it, so we used to specify it in 'Top Organization'. But in this scenario, we may need to write a Custom security code to achieve this using CONNECT BY. Could you please let me know if using CONNECT BY in the custom sql code will affect performance? Else another option I have is to explicitly specify all the Child Organizations on