def METHOD_NAME(builder, docname, **kwargs):
    """Return a single toctree starting from docname containing all
    sub-document doctrees.
    It filters toctree and shows only subdocuments
    """
    env = builder.env
    doctree = env.get_doctree(env.config.master_doc)
    toctrees = []
    documentation_set = docname.split('/')[0]
    for toctreenode in doctree.traverse(addnodes.toctree):
        entries_to_remove = []
        for e in toctreenode['entries']:
            ref = str(e[1])
            ref_set = ref.split('/')[0]
            if ref_set != documentation_set:
                entries_to_remove.append(e)
        for entry in entries_to_remove:
            toctreenode['entries'].remove(entry)
        toctree = env.resolve_toctree(docname, builder, toctreenode, **kwargs)
        if toctree is not None:
            toctrees.append(toctree)
    if not toctrees:
        return None
    result = toctrees[0]
    for toctree in toctrees[1:]:
        if toctree:
            result.extend(toctree.children)
    env.resolve_references(result, docname, builder)
    return result