Trie Algorithm for Autocomplete and Suggest word

Currently I try using Trie for Suggest and Autocomplete algorithm.

public List<string> Suggest2(string str)
{
    List<String> result = new List<String>();
    TrieNode curr = root;
    foreach (char c in str.Trim().ToLower().ToCharArray())
    {
        curr = curr.GetChild(c);
        if (curr == null)
            return result;
    }

    Suggest2(curr, new StringBuilder(str), result);
    return result;

}

public void Suggest2(TrieNode curr,StringBuilder sbTemp, List<string> result)
{
    if (curr == null) return;
    if (curr.IsEnd) result.Add(sbTemp.ToString());

    foreach (char c in curr.Childs.Keys)
    {
        sbTemp.Append(c);
        Suggest2(curr.Childs[c], sbTemp, result);
        sbTemp.Length--;
    }
}

Any Suggestion to improve this algorithm except changing String to StringBuilder ?