I created sample for this. Hope it will help
data.txt
Employees/Administration/Teamleader
Employees/Administration/Manager
Employees/Sales/Manager
Employees/Sales/Executive
string []str = File.ReadAllLines(@"D:\data.txt");
TreeNode root = new TreeNode();
root.Text = "All";
foreach (string s in str)
{
string[] arr = s.Split('/');
TreeNode department = null;
if (!root.Nodes.ContainsKey(arr[1]))
{
root.Nodes.Add(arr[1], arr[1]);
}
department = root.Nodes[arr[1]];
department.Nodes.Add(new TreeNode(arr[2]));
}
treeView1.Nodes.Add(root);