From The Document Foundation Wiki
- under the Entries tab, select the level that you previously set (10);
- delete the unneeded elements in the Structure rule, click once on them then press the Suppr key;
- under the Styles tab, select the predefined level (10) and set the level 1 paragraph style to it (Table of contents level 1) so the layout is the same for this two levels in the table of contents ;
- press OK.