What is the name of the top-level parentless folder in a digital file system? root tree child subfolder

The name of the top-level parentless folder in a digital file system is ROOT.
The digital file system has a tree structure in which there is only one parentless folder(the root folder). The root folder has several subfolders, Each of these subfolders has seveal sub-subfolders and so on. 
The root folder is the parent of all subfolders.

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