TreeNode rootNode = new TreeNode("Root Node"); TreeNode childNode1 = new TreeNode("Child Node 1"); TreeNode childNode2 = new TreeNode("Child Node 2"); rootNode.Nodes.Add(childNode1); rootNode.Nodes.Add(childNode2); // Expand the root node before collapsing it rootNode.Expand(); // Collapse the root node to hide child nodes rootNode.Collapse();In this example, we create a tree view control that has a root node and two child nodes. We first expand the root node to show the child nodes, and then we collapse the root node to hide the child nodes. The package library for System.Windows.Forms.TreeNode Collapse is part of the .NET Framework's Windows Forms library.