private fun add_to_children(item: Boxed[Numeric])
	do
		if children.not_empty then
			var center = center
			assert center != null
			if center.x > item.right then
				if center.y > item.top then
					children[0].add(item)
				else if center.y < item.bottom then
					children[1].add(item)
				else
					self.data.add(item)
				end
			else if center.x < item.left then
				if center.y > item.top then
					children[3].add(item)
				else if center.y < item.bottom then
					children[2].add(item)
				else
					self.data.add(item)
				end
			else if center.y > item.top then
				self.data.add(item)
			else if center.y < item.bottom then
				self.data.add(item)
			else
				self.data.add(item)
			end
		end
	end