Explanation:

private void TasksNodes_Load(object sender, EventArgs e)
{
this.treeView1.Nodes.Add("Tasks");
try
{
DatabaseOperations dbopration = new DatabaseOperations();
//This class contains the logic of the Data operations
DataTable myTable = dbopration.LoadTasksTable();
//Loads Tasks from the Database
foreach (DataRow row in myTable.Rows)
{
if (!string.IsNullOrEmpty(row[1].ToString()))
{
TreeNode node = new TreeNode(@"Task: " + row[1].ToString());
this.treeView1.Nodes[0].Nodes.Add(node);
TreeNode node2 = new TreeNode(@"FullTaskName: " + row[2].ToString());
node.Nodes.Add(node2);
}
}
this.treeView1.Sorted = true;
this.treeView1.Nodes[0].Expand();
Cursor.Position = new Point(Location.X + 30, Location.Y + 30);
//Move the Mouse curser to the first Node
}
catch (OleDbException exp)
{
MessageBox.Show("Error: {0}" + exp.Errors[0].Message);
}
}

Now see how we are selecting the treeview node.

private void treeView1_DoubleClick(object sender, EventArgs e)
{
if (treeView1.SelectedNode.IsSelected)
{
this.SelectedTreePath = selectAllPath(this.treeView1.SelectedNode);
//SelectedTreePath is a string type Variable defined in the Class
this.DialogResult = DialogResult.OK;
//To close the Popup Form. otherwise remove this line
}
}

private string selectAllPath(TreeNode ThisSelectedNode)
{
string selcetedAbove = ThisSelectedNode.FullPath;
string selectedBelow = string.Empty;
foreach (TreeNode node in ThisSelectedNode.Nodes)
{
selectedBelow += selectedBelow + "\\" + node.Text;
}

return selcetedAbove + selectedBelow;
}

This will close the Treeview and selected nodes Text will be copied to the SelectedPath (Which is a string variable).