{branch} ... {/branch} is a condition for the body of a {tree}: its content renders when the current row of the tree has children, and is skipped when the row is a leaf. Its usual content is the list markup around a {recurse} - {branch}<ul>{recurse}</ul>{/branch} - so a leaf does not get an empty <ul></ul>.

An @else@ part renders for a leaf instead: a different icon, a link where a folder gets a toggle. The children are read from the field the tree's children= option names (children by default); a field that is missing or empty means no children.

The tag takes no parameters. It belongs inside a tree: under the strict syntax check a {branch} with no {tree} around it, or without its closing tag, is an error.