Modify Sphinx TOC tree

I found a low-tech solution: hide the children of the last item using CSS.

div.toctree-wrapper > ul > li:last-child > ul {
  display: none;
}

Perhaps not an ideal solution, but I've done something like this before using multiple toctree entries on the same page, something like:

####################
Presto Documentation
####################

.. toctree::
    :maxdepth: 2

    overview
    installation

.. toctree::
    :maxdepth: 1

    release

It's not ideal since most themes will add extra padding between the trees, but in my case that was better than having the huge list of nested items for certain pages.