CSC301: Tree code: Recursion going left and right [34/56]

    public int size () {
        return size (root, 0);
    }
    private static int size (Node x, int sz) {
        if (x != null) {
            sz = size (x.left, sz + 1);
            sz = size (x.right, sz + 1);
        }
        return sz;
    }

Recursion going left and right. Now computing the size of the tree.

Is this correct?

Here is a trace of an execution.