For WinHelp, you specify the contents levels for your headings here:
[HelpCntStyles] ; format = H (heading), T (topic), or B (both), + level (1..9) Heading 1=B2
See §17.12.2 Specifying heading formats and levels for contents.
Each entry in [HelpCntStyles] must correspond to an entry with property Contents in [HelpStyles]; for example:
[HelpStyles] Heading 1=Topic Contents
See §17.7.2 Assigning properties to formats for topics and hotspots.