private function leftRotateTree(TreeNode &$root)
{
// Pivot = Root.Left
$pivot = $root->getChild(1);
// Root.Right = Pivot.Left
$children = $root->getChildren();
$children[1] = $pivot->getChild(0);
// Pivot, rotation side
$root->setChildren($children);
// Pivot.Left = Root
$children = $pivot->getChildren();
$children[0] = $root;
$pivot->setChildren($children);
// Root = Pivot
$root = $pivot;
}
