I guess I can't edit my answer anymore but wanted to update and say I checked on my USB keyboard and checked all the shortcuts with Insert.

Insert Note as Parent - Works if you add Ctrl, Alt or Cmd to Shift+Ins

Insert Node as the first subnode - Works with Alt+Ins, also Ctrl+Ins and Cmd+Ins give this action

Insert Note as the last subnode - Can't make this work from the keyboard, always get Insert Note as the first subnode action

window.onkeydown doesn't register any event if you just press Insert, only when combined with Cmd, Alt/Option or Ctrl

Edit - Lots of edits

Insert might be tricky, it works fine if you have a USB keyboard plugged in that has an Insert key on it. But the built-in keyboard on a Macbook doesn't have an Insert key. Supposedly the way to simulate the insert key on a Macbook keyboard is Fn + Enter but Chrome seems to treat it just like hitting Enter normally.

I did some experimenting with window.onkeydown and it looks like the event generated for Fn + Enter is exactly the same as Enter except code="NumpadEnter" and location=3.