Could you please review the below document, and let us know if it helps.
"When you enable object instance tracking for a node, AppDynamics analyzes the heap to identify classes with the most instances on the heap. AppDynamics tracks the top 20 .NET framework classes and the top 20 application classes based upon the number of instances. Use object instance tracking to identify memory usage trends in classes with large numbers of instances."
For more details please review the below document.