BTool.ComPortTreeForm.RemoveAll C# (CSharp) Method

        public bool RemoveAll()
        {
            bool flag = false;
            if (tvPorts.Nodes != null)
            {
                foreach (TreeNode treeNode in tvPorts.Nodes)
                {
                    if (treeNode != null)
                    {
                        DeviceForm deviceForm = ((DeviceInfo)treeNode.Tag).DevForm;
                        deviceForm.DeviceFormClose(true);
                        deviceForm.Close();
                        treeViewUtils.RemoveTextFromTree((TreeView)tvPorts, deviceForm.devInfo.ComPortInfo.ComPort);
                    }
                }
            }
            else
                flag = false;
            return flag;
        }

 private void FormMain_FormClosing(object sender, FormClosingEventArgs e)
 {
     m_mutex.WaitOne();
     comPortTreeForm.RemoveAll();
     m_mutex.ReleaseMutex();
 }