public void ResetImages(int idx, TreeNode parent = null)
{
TreeNodeCollection nodes = Nodes;
if (parent != null)
{
parent.ImageIndex = idx;
parent.SelectedImageIndex = idx;
nodes = parent.Nodes;
}
foreach (TreeNode treeNode in nodes)
{
treeNode.ImageIndex = idx;
treeNode.SelectedImageIndex = idx;
ResetImages(idx, treeNode);
}
}