I want to add a new field in my work item similar to roll up column so that it automatically calculates my story points ,it should automatically calculate my story points from child work items just like how it does in backlogs ,I can see this in backlog but due to some reasons i need to add it in my work item ,I have tried adding story points in process section in organization settings but that need to be manually filled but I need a field that auto calculates just like rollup column in column options, is it possible?

I tried creating a filed in process section in organization settings and added a filed named story points in feature but that needs to be manually filled, I want it to be auto calculated like how we have rollup column i.e sum of story points option in column options in backlog.