1. Create a AutoAlloc<GeListHead> and add some child nodes. Store this in a GeDialog.
2. In your GeDialog create a TreeView. Set the TreeViewCustomGui->SetRoot( mygelisthead->GetFirst(), &treeviewfuncs, this));
3. In your TreeViewFunctions::GetFirst() { return root;}
4. When setting your treeview layouts, add a checkbox. layout.SetInt32(TREE_COLUMNS_CHECK, LV_CHECKBOX);
5. Implement the functions for IsChecked and SetCheck
6. Run your code and when you click on the checkbox it will enter an endless loop somewhere in the c4dplugins code.

The reason for this is (2). Instead of calling SetRoot(mygelisthead->GetFirst()...). I should have just passed in the GeListHead.

Then for (3) I should have returned the First element: GeListHead op = (GeListHead)root; return op->GetFirst();

With these changes it works, but that took a while to figure out.