When creating a nested folder structure, it would be more convenient to allow for multi-column select lists such that we can specify what named folders in layer 2, for instance, exist in a given folder in layer 1:

For a structure:

F1 | F2

a1 | b1

a1 | b2

a2 | b3

In folder a1, there are folders b1 and b2, and in folder a2, there is a folder b3.