temp.sidebarSubNav = COA
temp.sidebarSubNav {
  10 = HMENU
  10 {
    entryLevel = 1
    1 = TMENU
    1 {
        expAll = 1
        noBlur = 1
        stdWrap.cObject = COA
        stdWrap.cObject {
          10 = HMENU
          10 {
            special = rootline
            special.range = 1|0
            wrap = <h2>|</h2>
            1 = TMENU
            1.NO.doNotLinkIt = 1
          }
          20 = HMENU
          20 {
            entryLevel = 1
            1 = TMENU
            1 {
              expAll = 1
              noBlur = 1
              NO {            
                  ATagTitle.field = subtitle//title
                  ATagParams = class="sidebarNav"
                  stdWrap.htmlSpecialChars = 1       
              }
            }
          }
        }
        wrap = |
        NO {       
        }
    }
  }
}

This subnavigation shows the parent page as headline and then a simple list for the navigation links. The navigation is only shown if the current page has actually subpages.

Subnavigation with parent page title as headline

TYPO3