在C#中FInd树中的上一个节点

public class TreeNode
{
    public int Value { get; set; }
    public TreeNode Left { get; set; }
    public TreeNode Right { get; set; }
    public TreeNode Parent { get; set; }
}

public TreeNode FindPreviousNode(TreeNode node)
{
    if (node == null)
    {
        return null;
    }

    if (node.Left != null)
    {
        TreeNode previous = node.Left;
        while (previous.Right != null)
        {
            previous = previous.Right;
        }
        return previous;
    }
    else
    {
        TreeNode current = node;
        while (current.Parent != null && current.Parent.Right != current)
        {
            current = current.Parent;
        }
        return current.Parent;
    }
}