Question / Problem
How can I make TreeSize to export data to Excel in the same spreadsheet (same file)?
Answer / Solution
When using Excel as export format, TreeSize will create a spreadsheet with the current timestamp and save the data into this sheet.
If the same file is selected for another export, TreeSize will create another sheet and append it to the file, so you won't lose the data from the previous export.
You can also specify a "Default Export File", so you don't need to select a file, every time you want to export the data. This can be done either in the Options of TreeSize (Tools -> Options -> Columns/Export -> Excel Export -> Default Export File") or in the corresponding export dialog (File -> Export -> Export to Excel -> "Always use this filename and add a new sheet when exporting").
When the default file was defined, you can simply go to "File -> Export -> Export to Excel" and TreeSize will add the current scan data to its own Excel sheet, using the default export file.