How do display forms project in treeview ?

I'm going to assume that you need recursion, that your menu structure could have more than one level of nesting, like this:

Form1
    Form5
    Form6
Form2
    Form7
    Form8
        Form11
        Form12
            Form13
    Form9
Form3
Form4
    Form10

Code example: assume a main form, MainForm, on MainForm a ToolMenuStrip, menuStrip1, and a Button 'btnBuildTree.

// map TreeNodes to MenuItems ...
private Dictionary<TreeNode, ToolStripMenuItem> dctTSMenuToTNode;

private void MainForm_Load(object sender, EventArgs e)
{
    dctTSMenuToTNode = new Dictionary<treenode,>();
}

private void btnBuildTree_Click(object sender, EventArgs e)
{
    dctTSMenuToTNode.Clear();

    buildTree(menuStrip1.Items, treeView1.Nodes);
}

private void buildTree(ToolStripItemCollection menuItems, TreeNodeCollection tNodes)
{
    foreach (ToolStripMenuItem menuItem in menuItems)
    {
        menuItem.Visible = true;

        var newNode = new TreeNode(menuItem.Text);

        tNodes.Add(newNode);

        newNode.Name = (newNode.Level == 0)
            ? "x"
            : "X";

        dctTSMenuToTNode.Add(newNode, menuItem);

        // recurse if necessary
        if (menuItem.HasDropDownItems)
        {
            buildTree(menuItem.DropDownItems, newNode.Nodes);
        }
    }
}

private void treeView1_AfterSelect(object sender, TreeViewEventArgs e)
{
    TreeNode currentNode = e.Node;

    // for testing only
    MessageBox.Show(string.Format("Node: {0} Name: {1}", dctTSMenuToTNode[currentNode].Text, currentNode.Name));

    // your code to select/show Forms goes here
    // pull the Form Name out of the Dictionary
    switch (dctTSMenuToTNode[currentNode].Text)
    {
        case "Form1":
            // do something with Form1
            break;
        // write other case statements here
    }
}

Comments:

1. While this will work (try it): a better strategy would be to use a Dictionary where the Key Type is 'TreeNode, and the Value Type of the Key is 'Form a reference to each instance of the various Forms you create.

2. Curious question: why do you need both a TreeView and a Menu based representation of your App's Forms structure ?