telephone directory by passing 300 files having peolpe's name and numbers.ishould show ll numbers wihile giving digits

//Inserts Names into the Trie data structure
public static Node InsertNode(string name, Node root)
{
    //Is name null?
    if (string.IsNullOrEmpty(name))
        throw new ArgumentNullException("Null Key");

    //set the index, start inserting characters
    int index = 1;
    
    //key
    string key;

    //start with the root node
    Node currentNode = root;

    //loop for all charecters in the name
    while (index <= name.Length)
    {
        //get the key character
        key = name[index - 1].ToString(); 

        //does the node with same key already exist?
        Node resultNode = currentNode.Children.GetNodeByKey(key);

        //No, this is a new key
        if (resultNode == null)
        {
            //Add a node
            Node newNode = new Node(key, name.Substring(0, index));
            
            //If reached the last charaecter, this is a valid full name
            if (index == name.Length)
                newNode.IsTerminal = true;
            
            //add the node to currentNode(i.e. Root node for the first time)
            currentNode.Children.Add(newNode);

            //set as the current node
            currentNode = newNode;
        }
        else
        {
            //node already exist, set as tghe current node
            //and move to the next character in the name
            currentNode = resultNode;
        }

        //move to the next character in the name
        index++;
    }

    //all done, return root node
    return root;
}




//Find a node given the key("Jo")
public static bool Find(Node node, string key)
{
    //Is key empty
    if (string.IsNullOrEmpty(key))
        return true;//terminal Node

    //get the first character
    string first = key.Substring(0, 1);

    //get the tail: key - first character
    string tail = key.Substring(1);

    Node curNode = node.Children.GetNodeByKey(first);

    //loop until you locate the key i.e. "Jo"
    if (curNode != null)
    {
        return Find(curNode, tail);
    }
    else
    {
        //not found, return false
        return false;
    }
}