IsInRole() not checking for nested group membership, what am i missing

Question

Giving correct results for all the groups returned by "whoami /groups" but not for nested groups. For example userA is a member of a group A and group A is a member of Group B then it is returning true for groupName = A but not for groupName = B, ideally the user is also a member of group B so it should return true.

My code looks like this:

if (!(this.User.IsInRole(groupName)))
{
  throw new UnauthorizedAccessException("Access denied to: "+this.UserName);
}

What am i missing here??