how to get the sub iteration details in RTC API

hello Team

I have a timeline structure like this :

Compnents devlepment( Timeline)
     MainItearation(iteration)
            SubIteartion(iteartion)

Using RTC API i am able to get the iteration name MainItearation(iteration) from Compnents devlepment( Timeline)

But i am unable to get the subiteartion name (SubIteartion(iteartion)) from Compnents devlepment( Timeline)

Below is my code :
if(developmentLine.getName().equals("Compnents devlepment"))
               {
      
        // get all iterations for this timeline.

        IIterationHandle[] iterations = developmentLine.getIterations();

        for (IIterationHandle iIterationHandle : iterations) {
            IIteration iteration = fAuditableClient.resolveAuditable(
                    iIterationHandle, ItemProfile.ITERATION_DEFAULT, monitor);
       
            String itearationName = iteration.getName();
        
        }
         
How to get all the sub iteartions using clien API ??

Thank You