Elastic Search group by regex

Grafana Elasticsearch
1

In elastic search we have release fields with data such as:
CMSSW_11_0_CLANG_X_2019_06_01
CMSSW_11_0_CLANG_X_2019_06_02
CMSSW_11_0_CLANG_X_(…)
CMSSW_11_0_GEN4_X_(…)
(…)
CMSSW_11_0_X_(…)
CMSSW_10_6_X_(…)
CMSSW_10_5_X_(…)
(…)

I want to filter and group the fields based on the part without data ( ex. CMSSW_11_0_X, CMSSW_10_6_X). The image shows how the graph SHOULD look like. The query with regex to filter data works. However, I can not group by regex (red circle), it does not work. How can I achieve it?