Hi Huisheng,
It seems to me like you are describing the combination of a dynamic fork/join combo with a task for each branch. Is this correct? If not, can you enlighten us a bit more about the behaviour you are looking for?
Also, we made it very easy to implement nodes yourself and add them. So if you happen to have the implementation for what you want feel free to attach a patch so we can consider to add it to the codebase.
Regards,
Koen