How to set visibility of a Tree Node that is created at runtime in C#

Question

I am relatively new to WPF C#, and I'm trying to set the visibility of a tree node. The nodes are created at runtime so there is no code in XAML for each node. Am I able to do everything in C# without binding? I started by filling the tree with everything from a list, and based on other conditions, I hide certain nodes from the user so there is less for them to look at since it is a pretty extensive list. 

 

foreach (TreeViewItem sheetItem in sheetTreeView.Items)

{

   if (sheet.Id.ToString() == sheetItem.Tag.ToString())

   {

      sheetItem.Visibility.Hidden;   // Referencing Instance

   }

}

 

Since I'm referencing an instance of an item, it is asking that I qualify it with a type name instead.

What does this mean, and can I still set the visibility of a referenced item somehow?