Trying to use and condition in Linq Query with join and on C#

[simpledeveloper]

Hi I have a linq Query as below

Query A:
from a in violations
join b in programs on a.ViolationTypeId equals b.ViolationTypeId
join d in branches on b.BranchId equals d.BranchId
join e in subprograms on a.ViolationSubtypeId equals e.ViolationTypeId into es
from e in es.DefaultIfEmpty()
join f in nonUniquePenalties on a.ViolationSubtypeId equals f.ViolationTypeId && f.ParentViolationTypeId==a.ViolationTypeId
where a.ApplyUniquePenalty == true

And I have an another Collection with name: nonUniquePenalties, which has ViolationTypeId and ParentViolationTypeId. the problem that I have is: violations has two fields, ViolationSubtypeId which can be null and ViolationTypeId can not null. Now I want to left join nonUniquePenalties such a way that, if violations doesn't have ViolationSubtypeId , it has to check only for ViolationTypeId of violations and ParentViolationTypeId of nonUniquePenalties, if violations has ViolationSubtypeId and ViolationTypeId, linq has to check for ViolationSubtypeId of violations with ViolationTypeId and ViolationTypeId of violations with ParentViolationTypeId of nonUniquePenalties. Any help please? And it has to be left outer join with other collections, since if there is no values in nonUniquePenalties, still the lnq should yield records. I tried a little bit, but any help would be very helpful, thanks in advance.