System.StackOverflowException: 'Exception_WasThrown' using TreeView

Question

I am using VS2022(V17.1.6) 64bit and have a C# Winform with a TreeView control. This displays the hierarchical relationship between Product Categories and Products within each category - maximum nodes around 33,000. All working well with a subset of the actual Category/Product structure. On completion of basic testing, I switch on the display of the full Tree which configures and displays ok. I can expand and collapse the tree ok. However, part of the functionality in creating the tree is to allow the user to select all or a subset of the Category/Product nodes. My recursive code (to build a list of selected nodes) when it gets to around 7,500 nodes it generates the StackOverflow exception. I have 16GB of RAM - each node has around 200 characters of information associated with it. If my maths is correct I should be coming no where near maxing out my available memory. As you can see I have a terminating check at the beginning of my recursive function (at the crash point the vars are 7587 and 33159 respectively) so it is not in a recursive loop. I think my code is ok - does this look like a memory maxing out problem? BTW the 'TraverseDownProductTree' is identical to the shown code except for a test against "PROD" instead of "CAT". This works fine for small subsets of the tree (say 5000 nodes) so if it is a memory problem I will either have to cut down my 200 chars or buy more memory :-( thanks in advance

private void TraverseDownCategoryTree(int selectedTreeIndex, int lastSelectedTreeIndex)
    {
        if (selectedTreeIndex == (lastSelectedTreeIndex)) return;

        TreeNode currentNode = TreeSelectedNodesList[selectedTreeIndex++];
        if (currentNode.Name.StartsWith("CAT"))
        {
            int categoryId = ((LevelTag)currentNode.Tag).Id;
            SelectedCategoriesList.Add(categoryId.ToString());
            TraverseDownCategoryTree(selectedTreeIndex, lastSelectedTreeIndex);
        }
        else
        {
            // PROD nodes found so start creating the export file

            selectedTreeIndex--; // set index for the traverse down the products starting at the proper node i.e. the node that is being processed here
            TraverseDownProductTree(selectedTreeIndex, lastSelectedTreeIndex);
        }
    }