I know that body of Notes note is HTML, experimented with different variations of checklist with radio buttons but none worked. I tried to find source code of note on disk (hoping to replicate it) but could not. I found location where they are held on disk but could not find actual source.

In any case, as @Mockman suggested, scripting UI did the job:

tell application "System Events"
    tell process "Notes"
        delay 1
        key code 124 using {command down}
        keystroke return
        keystroke "l" using {command down, shift down}
        keystroke "Item 1"
        keystroke return
        keystroke "Item 2"
    end tell
end tell