foreach (var summaryOdd in odds)
{
    var category = new PlacedCategory();
    var eventId = summaryOdd.Championship;

    if (categories.Any(cat => cat.Name == eventId))
    {
        category = categories.First(cat => cat.Name == eventId);
    }
    else
    {
        category.Name = eventId;
        categories.Add(category);
    }

foreach (var summaryOdd in odds)
{
    var category = new PlacedCategory();
    var eventId = summaryOdd.Championship;

    category = FindOrCreateCategoryByEventId(categories, eventId);