SExp.cs

private static LinkedTree<SExpNode> BuildTree(string literal, params LinkedTree<SExpNode>[] subNodes)
{
    var node = new LinkedTree<SExpNode>(new SExpNode() { Literal = literal });
    foreach (var subNode in subNodes)
    {
        node.AddSubNodeLast(subNode);
    }
    return node;
}

private static LinkedTree<SExpNode> BuildTree(string literal, params string[] subLiterals)
{
    var node = new LinkedTree<SExpNode>(new SExpNode() { Literal = literal });
    foreach (var subLiteral in subLiterals)
    {
        node.AddSubNodeLast(BuildTree(subLiteral));
    }
    return node;
}