If we consider levels from 0 to L so it may be the case that each level's nodes are completely filled than inserting an element at leaf node may result into splitting it and one element is pushed to upper level, there again splitting happens(in one node) since those nodes are also filled and this phenomena repeats. when we reach to the root node it will also split into two nodes and and new root will be created.
total splitting = L(levels) + 1(root) + 1(new root)