Extjs TagField dropdown items persistent after selection

I’m currenly trying edit TagField behaviour so that the dropdown items stay in dropdown even after you select one or multiple. Use case is something like revenue calculator (every user can determinate own math formula given some constants and math operators), so user can select f.e. symbol “+” multiple times to get formula they want. Is there a easier way then f.e. after selection add the record back to store? Is there better component for something like this?

As I described earlier I only tried TagField and not that pretty code after every selection. I bet there is better way to do it, I’m kidna new to Extjs. Thanks for every suggestion 🙂