@Override
  public RealizationResult create(Region regionConfig, InternalCache cache) {
    RegionConfig xmlConfig = converter.fromConfigObject(regionConfig);
    return create(xmlConfig, regionConfig.getName(), cache);
  }
this is used to create only root regions.

@param regionConfig the name in the regionConfig can not contain sub-regions.
geode-core/src/main/java/org/apache/geode/management/internal/configuration/realizers/RegionConfigRealizer.java