Help to understand explain plan in Oracle
Explain plan does not tell you what is actually the most costly "operation". The "Cost" column is a guess - it is a value estimated by optimizer. So is "Cardinality" column and "Bytes" column. http://docs.oracle.com/cd/B28359_01/server.111/b28274/ex_plan.htm#i18300

In your example, your optimizer tells you:  I decide to use this plan because I guess that looping would cost about 5,483. And I hope this would be the most costly part of the execution, but I can't guarantee this.

The same applies recursively to all the depths of the tree.

If you go in-depth to the lowest levels (that is by intuition most-looped, most-executed levels) you see that the operation that especially sticks out, both in terms of expected cost and expected number of elements, is the

6 INDEX RANGE SCAN INDEX RAIDPIDAT.IDX_HISTORY_STATE_TABLE_1TPALM Cost: 662  Cardinality: 102,068 


So, optimizer guessed that optimal execution of this query is to loop a lot around a poor workhorse RAIDPIDAT.IDX_HISTORY_STATE_TABLE_1TPALM. I really cannot see which part of your query directly relates to it, but I suspect t1.data_tratado condition. And, again, I cannot see if it is really the most costly part.

I'll try to translate the syntax of loops in the explain plan to procedural pseudo-code:

/* begin step 13 (by "step 13" I mean a line that reads "   13 NESTED LOOPS") */
  /* begin step 7 */
    do step 5
    myresult = rows from step 5
    for each row from myresult {
       do step 6
       for each row from step 6 {
           join to a row from myresult the matching row from step 6
       }
    }
  /* end step 7 */
  for each row from myresult {
     do step 12
     for each row from step 12 {
         join to a row from myresult the matching row from step 12
     }
  }
/* end step 13 */
return myresult


Seems complicated, but really aim of each "nested loop" is to create a join (a single table made of two tables) in the most naive way, a loop-inside-a-loop.