How to expand all the subsections on the sidebar toctree in Sphinx?

I was wondering if there is a way to expand all the subsections under the headers that are included in the index.rst file?

As an example, here is how it is:

Section 1
Section 2
Section 3

And here is how I would like it to be:

Section 1
  Subsection 1.1
  Subsection 1.2
  Subsection 1.3
Section 2
  Subsection 2.1
  Subsection 2.2
  Subsection 2.3
Section 3
  Subsection 3.1
  Subsection 3.2
  Subsection 3.3

If I click on Section 1, it shows what's under that, but if I click on Section 2, contents of section 1 are hidden and only 2 is shown. I would like all 2 sections to be expanded every time I'm on the index page. I've tried adding toctree and maxdepth, nothing works.