dir /s /b /o:gn

or

dir /s /b /o:gn > C:\Temp\result.txt

Flag description:

• /S :: displays files in specified directory and all subdirectories
• /B :: Uses bare format (no heading information or summary)
• /O :: List by files in sorted order
• :gn :: g sorts by folders and then files, and n puts those files in alphabetical order