If child nodes are manually expanded, one of those nodes might have other parent nodes that are not yet visible. In this case, the existence of further hidden parent nodes should be communicated to the user e.g. by a plus sign button at the top of the node.
Clicking this button should expand all direct parent nodes (no parents of parents etc.).
If those expanded parent nodes have further child nodes that are already visible, the edges between them should be displayed.
If child nodes are manually expanded, one of those nodes might have other parent nodes that are not yet visible. In this case, the existence of further hidden parent nodes should be communicated to the user e.g. by a plus sign button at the top of the node. Clicking this button should expand all direct parent nodes (no parents of parents etc.). If those expanded parent nodes have further child nodes that are already visible, the edges between them should be displayed.