Find lowest leaf nodes in a binary tree

So this is probably a popular problem, and I decided to take a crack at it today using C#.

I came up with the following solution:

private  BinaryTree.BinaryTreeNode FindLowestNodes(BinaryTree.BinaryTreeNode node, int depth, ref int biggestDepth) {
    this.WriteResult("Entering recursiorn for node.....{0}", node.Value.ToString());
    BinaryTree.BinaryTreeNode lowestNode = null;
    if (node.Left != null) { 
        var n = FindLowestNodes(node.  Left, depth + 1, ref biggestDepth);
        if (n != null) lowestNode = n;
    }
    if (node.Right != null) { 
        var n = FindLowestNodes(node.Right, depth + 1, ref biggestDepth);
        if (n != null)
            lowestNode = n;
    }
    if (node.Left == null && node.Right == null) {
        if (depth > biggestDepth) { 
            lowestNode = node;
            biggestDepth = depth;
        }
    }
    return lowestNode;
}

This is a recursive function using a depth parameter, and biggestDepth parameter that helps me determine if the node is indeed the lowest since the tree can have multiple depths. What I don't like about passing an int by reference is boxing...

Could this solution be written more efficiently?

Also, would it be easier to parallelize using a functional language like Clojure, or is that not really a factor as long as variables are not passed by reference?

Passing an int with the ref keyword does not involve any boxing at all. Do not confuse this with "passing an int by reference" (as in, a function with return type Object returning an int,) which is quite a different thing, and it does involve boxing.

Your code seems quite efficient to me, I have nothing to comment on.

StackExchange Code Review Q#7564, answer score: 2