Behavior Tree Composite with two slots/connectors.

Hello!
The Simple Parallel composite in the Behavior Tree has two slots (or connectors) at the bottom: one for the main task and one for background tasks. They are visually separated in the Behavior Tree editor.
I want to create my own custom Composite which should also have two separate slots/connectors for two different types of tasks. How I can achieve this? I looked at the source code of BehaviorTree/Composites/BTComposite_SimpleParallel.cpp but I don’t see anything that defines this change in display. I even tried deriving my custom composite from BTComposite_SimpleParallel but it still only shows one single large connector at the bottom of the node.
I understand that the main task is simply the child at index 0, and that is fine. But I would prefer if the node displayed in the behavior tree would make this apparent by visually separating child 0 from the rest in separate slots/connectors at the bottom of the node.
Thank you!