C# :: Treeview Node Selection Show First Node Of Tree Instead Of Selected

I am working on C# Project [Windows Form Application], to update treeview nodes from excelsheet [xls] Cell [row i, Column 3] Values, while on selecting treenode, it should update corresponding Column 4 Value [row i, Column 4]. For me, Treenode are populated successfully, but on selecting the treenode, it always display first Element of treenode [Not selected one].

Populated Treenode from Excel as: [ Update Child Nodes from Column 3 elements [Column 2 Contain Parent node name and Column 3 have Child Node name], if Column 2 Value is same as Parent node name [My Module], update the child nodeunder same Parent node.]

for (int i = 0; i < worksheet.UsedRange.Rows.Count; i++) {
string mynode = ((Excel.Range)worksheet.Cells[i + 1, 3]).Value2.ToString();
string mynode2 = ((Excel.Range)worksheet.Cells[i + 1, 2]).Value2.ToString();

[Code] ....

On selecting the Child Node, it always give 1st Parent node. Instead of Selected Node.

for (int i = 0; i < worksheet.UsedRange.Rows.Count - 2; i++) {
string mynodetext = ((Excel.Range)worksheet.Cells[i + 2, 3]).Value2.ToString();
string mynodetext1 = ((Excel.Range)worksheet.Cells[i + 2, 4]).Value2.ToString();
if (treeView1.SelectedNode.FirstNode.Text == mynodetext) {
this.richTextBox1.SelectedText += Environment.NewLine + mynodetext1 + Environment.NewLine;
}
}

How to get correct selected Node.