Expanded state of a new tree row: a fixed value for all rows, or a function per row (e.g. (_data, deep) => deep < 1 → only the top level is open).
(_data, deep) => deep < 1
Expanded state of a new tree row: a fixed value for all rows, or a function per row (e.g.
(_data, deep) => deep < 1→ only the top level is open).