static void Main()
{
var items = new IDataItem[] {
new TestItem(),
new TestItem(),
new TestItem2(),
new TestItem2(),
};
foreach (var kv in items.GroupBy(c => c.GetType()))
{
// group by actual type
var type = kv.Key;
var batch = kv.ToArray();
// grab BulkInsert<Type> method
var insert = typeof(Test).GetMethod("BulkInsert").MakeGenericMethod(type);
// create array of Type[]
var casted = Array.CreateInstance(type, batch.Length);
Array.Copy(batch, casted, batch.Length);
// invoke
insert.Invoke(new Test(), new object[] { casted });
}
Console.ReadKey();
}