*/
private rbInsertLeft(node: TreeNode | null, p: Piece): TreeNode {
z.left = SENTINEL;
z.right = SENTINEL;
z.parent = SENTINEL;
z.size_left = 0;
z.lf_left = 0;
if (this.root === SENTINEL) {
this.root = z;
z.color = NodeColor.Black;
node!.left = z;
z.parent = node!;