Something like:
{{ define "souspages" }}
{{ if .Pages }}
<ul>
{{ range .Pages}}
<li><a href="{{ .Permalink }}">{{ .Title }}</a>
{{ template "souspages" . }}
</li>
{{ end }}
</ul>
{{ end }}
{{ end }}
<ul>
{{ range .Site.Sections }}
<li><a href="{{ .Permalink }}">{{ .Title }}</a>
{{ template "souspages" . }}</li>
{{ end }}
</ul>
souspages
is subpages
in French.