a problem with add nodes to treeview

[bill]

0- (nodename) text1 4 text1 4
1 |-4 (node_parentname) text2 0 text2 5
2 OK fail
3

private void button1_Click(object sender, System.EventArgs e)
{
TreeNode leaf=new TreeNode(textBox1.Text);//create node
leaf.Tag=textBox2.Text;//node's father

treeView1.BeginUpdate();
addsub(treeView1.Nodes,leaf);
treeView1.EndUpdate();
}

public void addsub(TreeNodeCollection root,TreeNode leaf)
{
for(int i=0;i<root.Count;i++)
{
if(root[i].GetNodeCount(true)>0)//if has sub node do recursion,but may
be here is wrong
addsub(root[i].FirstNode.Nodes,leaf);
else if(root[i].Text==leaf.Tag.ToString())
root[i].Nodes.Add (leaf);
}
}