Add custom workflow to solution in Dynamics CRM

When I try to add a custom workflow to an unmanaged solution by "Add Existing" button, it is done successfully.

But we I try to add the SAME workflow in code c# with "AddSolutionComponentRequest", it throws this error :

Subcomponent 21a41b15-9bf2-e611-80de-1458d0432720 cannot be added to the solution because the root component Workflow is missing.

Any help please.