As per Salesforce documentation, 5 levels of categories are supported. Following code is giving information only about category with name Group_Category, but no information about child categories are returned. Is there a way to pull information about child categories using describe call.
List <DataCategoryGroupSobjectTypePair> pairs = new List<DataCategoryGroupSobjectTypePair>();
DataCategoryGroupSobjectTypePair pair = new DataCategoryGroupSobjectTypePair();
pair.setSobject('KnowledgeArticleVersion');
pair.setDataCategoryGroupName('Group_Category');
pairs.add(pair);
List<Schema.DescribeDataCategoryGroupStructureResult> groupResult = Schema.describeDataCategoryGroupStructures(pairs, true);
System.debug('groupResult:::' + groupResult);