Yes, you can definitely collapse rows in Excel and leave a plus sign to open/close them. Here's how you can do it:

1. Select the rows that you want to collapse.
2. Right-click on the selected rows and choose "Group" from the drop-down menu.
3. A dialog box will appear asking you whether you want to group the selected rows or columns. Make sure that "Rows" is selected and click "OK".
4. You will notice that a small plus sign has appeared in the left-hand margin of your worksheet, next to the row numbers. Clicking on this plus sign will collapse the grouped rows.
5. To expand the grouped rows again, simply click on the minus sign that has replaced the plus sign.

That's it! You can now collapse and expand your grouped rows using the plus and minus signs. This is a great way to organize your data and make it easier to navigate.