A call hierarchy of a function invocation is a very useful tool to quickly navigate in code. In VSCode I find my self using "Find Reference" repeatedly to do what I do with a call hierarchy in IDEs (Eclipse, IntelliJ). UI-wise I think it could fit nicely with how "Find References" is done, but of course we would need to have a tree on the right hand side and the labels need to display the reference containing function definitions. Conceptually it is close to a type hierarchy, which is requested in #15533.