select v, p, sum(am2) am from (
select v,p, level, xx_sql.query('select '||sys_connect_by_path('('||to_char(am)||')','+')||' from dual') am2 
from (
select 1 v , 0 p, 0 am from dual
union all
select 2 v, 1 p, 120.2 am from dual
union all
select 4 v, 2 p, -75 am from dual
union all
select 5 v, 2 p, 23 am from dual
union all
select 3 v, 1 p, 210 am from dual  
) t
connect by v = prior p
--start with p = 0 -- не указываем откуда собираем
) group by v,p

select v, p, 
       xmlcast(xmlquery(max(sys_connect_by_path(am,'+')) returning content) as number) result,
       max(sys_connect_by_path(am,'+')) str
from (
select 1 v , 0 p, 0 am from dual
union all
select 2 v, 1 p, 120.2 am from dual
union all
select 4 v, 2 p, -75 am from dual
union all
select 5 v, 2 p, 23 am from dual
union all
select 3 v, 1 p, 210 am from dual  
) t
connect by v = prior p
--start with p = 0
group by v,p
order by 1

with t(id, parent_id, description, amount) as
(
  select 1 id, null, 'top', 10  from dual
  union all select 2, 1, 'top-one', 100 from dual
  union all select 3, 2, 'one-one', 2000 from dual
  union all select 4, 2, 'one-two', 3000 from dual
  union all select 5, 1, 'top-two', 1000 from dual
  union all select 6, 2, 'one-three', 300 from dual
  union all select 7, 6, 'three-one', 1 from dual
)
, h as
(
  select id, parent_id, description, amount, level l, rownum rn
    from t
   start with id = 1
 connect by parent_id = prior id
)
select *
  from (select h.*,
               power(2 * 10, 1 - l) x,
               sum(power(2 * 10, 1 - l)) over(order by rn) s
          from h) h0
match_recognize
(
  order by rn
  measures
    first (id) as id,
    first (parent_id) as parent_id,
    first (l) as l,
    first (rn) as rn,
    first (amount) as amount,
    final count(*)-1 cnt_children,
    final sum(amount) h_sum
  one row per match
  after match skip to next row
  pattern (y+)
  define
    y as sum(x) < 2 * first(x)
    --ORA-03113, 12.1.0.2
    --y as max(s) - min(s) < first(x)
) mr;

        ID  PARENT_ID          L         RN     AMOUNT CNT_CHILDREN      H_SUM
---------- ---------- ---------- ---------- ---------- ------------ ----------
         1                     1          1         10            6       6411
         2          1          2          2        100            4       5401
         3          2          3          3       2000            0       2000
         4          2          3          4       3000            0       3000
         6          2          3          5        300            1        301
         7          6          4          6          1            0          1
         5          1          2          7       1000            0       1000

7 rows selected.

with t(id, parent_id, description, amount) as
(
  select 1 id, null, 'top', 10  from dual
  union all select 2, 1, 'top-one', 100 from dual
  union all select 3, 2, 'one-one', 2000 from dual
  union all select 4, 2, 'one-two', 3000 from dual
  union all select 5, 1, 'top-two', 1000 from dual
  union all select 6, 2, 'one-three', 300 from dual
  union all select 7, 6, 'three-one', 1 from dual
)
, h as
(
  select id, parent_id, description, amount, level l, rownum rn
    from t
   start with id = 1
 connect by parent_id = prior id
)
select *
  from (select h.*,
               power(2 * 10, 1 - l) x,
               sum(power(2 * 10, 1 - l)) over(order by rn) s
          from h) h0
match_recognize
(
  order by rn
  measures
    final count(*)-1 cnt_children,
    final sum(amount) h_sum,
    count(*) cnt
  all rows per match
  after match skip to next row
  pattern (y+)
  define
    y as max(s) - min(s) < first(x)
) mr
where cnt = 1;

        RN CNT_CHILDREN      H_SUM        CNT         ID  PARENT_ID DESCRIPTI     AMOUNT          L          X          S
---------- ------------ ---------- ---------- ---------- ---------- --------- ---------- ---------- ---------- ----------
         1            6       6411          1          1            top               10          1          1          1
         2            4       5401          1          2          1 top-one          100          2        .05       1.05
         3            0       2000          1          3          2 one-one         2000          3      .0025     1.0525
         4            0       3000          1          4          2 one-two         3000          3      .0025      1.055
         5            1        301          1          6          2 one-three        300          3      .0025     1.0575
         6            0          1          1          7          6 three-one          1          4    .000125   1.057625
         7            0       1000          1          5          1 top-two         1000          2        .05   1.107625

7 rows selected.