code: protected ExpandDataTrunk getExpansion(final String expansionName, final Map<String, Collection<String>> subExpansionNames) {
          final ExpandDataTrunk expandData = new ExpandDataTrunk(new ExpandDataDetails(expansionName));
          // Add the sub expansions
          expandData.setBranches(getExpansionBranches(subExpansionNames));
          return expandData;
      }
docs: Create an expansion with sub expansions.
  
  @param expansionName The name of the root expansion.
  @param subExpansionNames The list of names to create the branches from.
  @return The expansion with the branches set.