How to implement a virtual directory

#1

The file structure is：

--folderA
    -- folderB
      -- file4.txt
    -- file1.txt
    -- file2.txt
    -- file3.exce

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want to navigate the tree structure is：

--folderA
    -- folderB
      -- TXT
        -- file4.txt
    -- TXT
      -- file1.txt
      -- file2.txt
    -- EXCEL
      -- file3.excel

‘TXT, EXCEL’ is a virtual existence. In fact, for classification display.Preformatted text