public void notifySectionInserted(int sectionIndex) {
        if (sections == null) {
            buildSectionIndex();
            notifyAllSectionsDataSetChanged();
        } else {
            buildSectionIndex();
            Section section = this.sections.get(sectionIndex);
            notifyItemRangeInserted(section.adapterPosition, section.length);
        }

        updateCollapseAndSelectionStateForSectionChange(sectionIndex, +1);
    }
Notify that a new section has been added

@param sectionIndex position of the new section
android/modules/module_common/src/main/java/github/tornaco/android/thanos/widget/section/SectioningAdapter.java