private void CallAutoBalance() { if (selectedNodes.Count != 0) { if (selectedNodes.ElementAt(0) is BSTViewModel) { Tree treeTest = new Tree(selectedNodes,Lines); if (treeTest.hasIntKeysAndBSTNodes()) { undoRedo.InsertInUndoRedo(new AutoBalanceCommand(treeTest, Nodes, selectedNodes, Lines)); } } else if (selectedNodes.ElementAt(0) is T234ViewModel) { if (validT234Tree()) { undoRedo.InsertInUndoRedo(new AutoBalance234(Nodes, selectedNodes, Lines)); } }else System.Windows.MessageBox.Show("Tree contains red/black nodes."); } }