You cannot export a complete merchandise hierarchy to a single CSV file. You can however, export the following merchandise hierarchy elements to individual CSV files:
Merchandise hierarchy versions
Merchandise hierarchy levels
Merchandise hierarchy nodes
You can export the merchandise hierarchy elements from their list pages. Click the Export - CSV icon to export the contents of the list. Only the fields displayed in the list will be exported to CSV. For more information, see the Exporting Reports, Searches, and Lists topic.