How can I use the same NERDTree buffer for directory listings and the sidebar?

How can I use the same NERDTree buffer for directory listings and the
sidebar?

When opening a directory in vim, NERDTree pops up with a directory
listing. Toggling the NERDTree opens a sidebar with a directory listing in
a new buffer.
As a result, any changes made in the initial buffer do not carry over to
the sidebar (e.g. expanding/contracting nodes). I use the initial buffer
to open the first file I'll be working on (often in a sub-directory), so I
find this very tedious.
Ordinarily, using :NERDTreeToggle ensures that NERDTree uses only a single
buffer for the sidebar, but there doesn't seem to be any option to use the
same buffer as the initial directory listing.
To illustrate: