AFAIR you can do this, but it's buggy. Can't remember the method (google it!).
Best thing is to manually move from smaller folders into the main one, it also gives one a chance to manually check for conflicts (e.g. files with same name and the version of the same file is the one you actually want), BEFORE dumping a whole folder's contents into another. Otherwise you simply get a nondescript op-up saying something like "File x is already in this folder, do you want to replace: Yes / Stop" before it moves on to the next conflict.