If you want to open the top-level and get a list of its subfolders, use the following button as a template using your own path, using the includestart argument:
<?xml version="1.0"?>
<button 3dborders="no" backcol="none" display="both" icon_size="large" label_pos="right" popout="right" textcol="none" type="menu">
<label>List C: Folder</label>
<icon1>#folder</icon1>
<button 3dborders="no" backcol="none" display="label" icon_size="large" label_pos="right" textcol="none">
<label>List C: Folder</label>
<tip>List C: Folder</tip>
<icon1>#folder</icon1>
<function type="normal">
<instruction>Go C: FOLDERCONTENT=dblclickmenu,nofiles,includestart,"maxwidth=45" NEWTAB=findexisting</instruction>
</function>
</button>
</button>
The old method before the includestart became available was shown in