Is it possible to cancel collapsing of nodes at certain nodes, or just mark nodes, that recursive collapsing should stop at those?

I got multiple trees, which should be collapsed to their root node, so I iterate through every node, check if it is a root node (derived class from DiagramNode) and collapse it. So far it works.

But those root nodes can also be connected together to indicate a process workflow.

Root --> Root2 --> Root3
 |         |         |
 v         v         v
Child    Child     Child
 

Since those connection also count as "incoming" links, the connected processes will also be collapsed. Is it somehow possible to mark those root nodes, that recursive collapse should stop at those or does an event exists, at which I can cancel the child recursion?

Thanks for the direction, but I don't use expand buttons for collapsing the nodes.

Instead the collapsing is triggered by a command from the ribbon, which iterates through all nodes, and collapses them if they're "root node"-types.

I solved my problem for now, by reiterating through the nodes after the collapse, and set the nodes to visible if they are a root node (same for the links, connecting the root nodes). Not the most elegant solution, but it works for me for now.