getItemSize = item =>
	// Each item takes 1 line
	// + the size of the children
	// + 1 extra line when it has children and filteredChildren
	!item.children
		? 1
		: item.filteredChildren
			? 2 + getTotalSize(item.children)
			: 1 + getTotalSize(item.children)
@template T
@param {Children<T>} item item
@returns {number} item size