How to restrict Parent folder from Child folders users?

Hi,

I am working on Sharepoint with C#.

I am facing issue related Folder access permission.

Here is the scenario: 

I have 1 parent folder (name as P1) with 3 user permission (a, b and c), and I am creating 1 child folder (Ch1) with 2 user permission(x,y) inside P1 folder. By default Ch1 folder should be accessible of all 5 users(3 from P1 and 2 from Ch1). But I want to restrict P1 folder from Ch1 folder's (users - x, y). 

How can I achieve it with C#. ?

Please someone have idea about it please share it.