[SOLVED] In React Dev Tools Profiler Flamegraph, what is an "Insertion" component?

In React Dev Tools Profiler Flamegraph, what is an "Insertion" component?

If I run the React dev tools profiler, and then look at the flamegraph, I can see various react components and their rendering times. Such as

ForwardRef(DataGridPremium) (<0.1ms of 1996ms)
GridContextProvider (<0.1ms of 1996ms)
MuiTextFieldRoot (<0.1ms of 229ms)

But there is also an item listed as if it was a react component, called Insertion, with a render time:

Insertion (528ms of 528ms)

It looks like this in a flamegraph, with an orange background:

I've found nothing in the react docs, the react dev tool docs, or on google. Many results bring me to useInsertionEffect but I don't think that's related as we have statically compiled CSS to the best of my understanding.

What is this Insertion? Is it a component? I obviously could guess that it means the time to insert DOM nodes, but I don't want to make assumptions. There's no components in our codebase that match this name, nor in our libraries it seems, from a grep.

Edit: I did find this in @mui/material/umd/material-ui.development.js:4730, perhaps it's that? I'd like to find a way to confirm that if possible, so I can investigate why it's our longest time to render thing.

  var Insertion = function Insertion(_ref) {
    ...
  }

Solution