The instance retention graph only shows the shortest path to a root node. This is also documented:
"The instance retention graph only shows the shortest chain of references from each GC root to your selected object. When you break this chain of references, the object may still be kept in memory by a longer chain of references.
After you have modified your code to break the first chain of references, profile your application again; the instance retention graph updates to show the chain of references which is now the shortest chain. You will need to modify your code again, to break this chain of references, and repeat until all the chains of references are broken and the object is no longer in memory."
However, I would like to see all paths that lead from a node to a root node. Is that possible?