Share 'adding growing data'

hello all,I have a small problem. I have a counter set on 50 ms, and every 50 ms I a get a different value, a single double. I was wondering if there is a possibility to create a growing tree or list, each 50 ms one item more to mass-add all of the incoming values. the mass addition is not working with single changing values, it needs a list with items. I hope someone can help...