
- Item up/down (within a single tree only - with removable stops at least)
- Move item (to any branch, with an appropriate rebuild)
- Rebuild tree (fix it when stuff gets out of step)
- Delete item (with option to recursively remove descendants)

- Various queries:
  - Parent (done)
  - Root
  - Siblings (done)
  - Ancestors (done)
  - Descendants
  - Previous sibling (done)
  - Next sibling (done)
  - etc.
