Nested collections root index.md long saving time

Hi all,

When using Nested Collections with 11ty, and a larger site, the root `index.md` file takes an age to save.

Upon investigation, it seems as when triggering a publish, it sends a `POST` request to `/.netlify/git/github/git/trees`, which includes a payload of a tree of every file on the same level as that root `index.md` (which is the whole site).

This obviously is a standard setup for sites using 11ty, but wondered if this was a bug. Obviously, as a workaround I can move the root `index.md` file to a subfolder, and change the permalink, but then the client loses control of the `path` within Netlify.

Any advice is much appreciated - thanks!

Start by reproducing the slow save with an 11ty site using Nested Collections and a root index.md, then inspect the publish request to /.netlify/git/github/git/trees. Compare the tree payload with a root index.md in a subfolder. Done means the root file saves without sending the entire site tree while retaining client control of its path.

Written by the indexing model from the issue text.