Design and format an insert leaflet

I have a children’s book with internal pages sized 15 cm x 15 cm.
I would like to add an insert leaflet inside the book. The leaflet should be slightly taller, so that its title appears above the book when closed — visible from the top edge.

The leaflet dimensions should be approximately 15 cm wide x 17–18 cm tall (2–3 cm taller than the book).

The text I have will fit into about 10 pages with this size, meaning the leaflet will have 5 folded spreads (5 sheets / 10 pages total).

Requirements:
Format the leaflet for print (ready-to-print PDF).
Include 5 folds / 10 pages in total.
The title should appear at the top (in the extra 2 cm area that sticks out only above the book).
Use the text I provide.
Maintain professional print margins and layout.

Preferably deliver both the print-ready PDF and the editable source file (InDesign / Word , etc.).

Deliverables:

Print-ready PDF file (15 x 17 cm or 15 x 18 cm, with bleed if needed).
Editable file format.
Layout with clear page breaks (10 pages total).
Title positioned vertically (or horizontally) at the top margin, visible when inserted inside the 15x15 cm book.