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Adding nodes to a specific parent node in a treeView (c#)
using (var reader = File.OpenText("Configuration.ini"))
            {
                List<string> hostnames = ParseExternalHosts(reader).ToList();
                foreach (string s in hostnames)
                {
                    TreeNode newNode = new TreeNode(s);
                    hostView.SelectedNode.Nodes.Add(newNode);
                }

const string nodeKey = "hostNode";

TreeNode tn1 = new TreeNode("My Node");
tn1.Name = nodeKey; // This is the name (=key) for the node.

TreeNode tn2 = new TreeNode("My Node2");
tn2.Name = "otherKey"; // This is the key for node 2.

treeView1.Nodes.Add(tn1); // Add node1.
treeView1.Nodes.Add(tn2); // Add node2.

// Find node by name (=key). Use the key specified above for tn1.
// If key is not unique you will get more than one node here.
TreeNode[] found = treeView1.Nodes.Find(nodeKey, true);

// Do something with the found node - e.g. add just another node to the found node.
TreeNode newChild = new TreeNode("A Child");
newChild.Name = "newChild";

found[0].Nodes.Add(newChild);