with t as
 (select 1 id, sysdate ds, sysdate + 10 de
    from dual
  union all
  select 2 id, sysdate + 5, sysdate + 15
    from dual
  union all
  select 3 id, sysdate + 11, sysdate + 16
    from dual
  union all
  select 4 id, sysdate + 12, sysdate + 17
    from dual
  union all
  select 5 id, sysdate + 12, sysdate + 17
    from dual
  union all
  select 6 id, sysdate + 18, sysdate + 19
    from dual
  --union all
  --select 7 id, sysdate + 18, sysdate + 19 from dual
  ),
t1 as
 (select t.*,
         lag(t.ds) over(order by ds) ds_prev,
         row_number() over(order by ds, de, id) r
    from t),
t2(id, ds, de, ds_prev, r, idroot, rroot) as
 (select id, ds, de, ds_prev, r, t1.id, t1.r
    from t1
  union all
  select t1.id, t1.ds, t1.de, t1.ds_prev, t1.r, t2.idroot, t2.rroot
    from t2
    join t1
      on t1.ds > t2.de
     and t1.ds_prev <= t2.de)
select t2.*, dense_rank() over(order by t2.idroot) gr
  from t2
 where not exists (select 1
          from t2 tt
         where t2.id = tt.id
           and tt.rroot < t2.rroot)