Creating a subitem by modifying the item title

Select the item.

the selected item is shown

Edit the title by pressing F2 or using the menu

text box showing the item title

Edit the text, using ' \ ' to separate the item's and the subitem's titles

text box showing the edited item title

Press Enter or click Ok to realize

the new item appears under the earlier item

The text on the right hand size is copied from the original item. You can change it...

the subitem's text is changed

... and go back to the original item to see that that still has the same text

the item's text is still the same

Note that it's possible to create several sublevels at once by using multiple backslashes.