Finding childless nodes

DAX has a number of parent-child functions, including PATH, PATHCONTAINS, PATHITEM, PATHITEMREVERSE, and PATHLENGTH. These functions help us analyze data presented in the format of a parent-child hierarchy. While the parent-child functions help us determine such things as the entire lineage of rows of parent-child hierarchy data, the number of levels within a hierarchy, and who is the n^th level down in the hierarchy, there is some useful functionality that is not included. For example, it can be useful to know the top and bottom levels of the hierarchy or, essentially, where hierarchies begin and end. Determining the top level of a hierarchy is very easy: we simply need to filter for the row or rows that have no parent. However, finding the bottom of the hierarchy, nodes that have no children, is somewhat more difficult since these may occur at any level...