Selecting the root nodes v17

The START WITH clause determines the rows selected by table_expression to use as the root nodes. All rows selected by table_expression where start_expression evaluates to true become a root node of a tree. Thus, the number of potential trees in the result set is equal to the number of root nodes. As a consequence, if the START WITH clause is omitted, then every row returned by table_expression is a root of its own tree.