(C#) Problem With Random Number Generator

  private int randomIndex = 0;
     public void GiveIndex()
     {
         float randomValue = Random.value;
         if (randomIndex >= 0 && randomIndex < 5)
         {                                                                                                        // FIRST SET starts here
             if (randomValue <= 0.5) { randomIndex = 0; }
             if (randomValue > 0.85) { randomIndex = Random.Range(1, 5); }
             if (randomValue > 0.5 && randomValue <= 0.85) {randomIndex = 5;}        
         }                                                                                                       // FIRST SET ends here
         
         if (randomIndex >= 5 && randomIndex < 11)
 
         {                                                                                                      // SECOND SET starts here 
             if (randomValue <= 0.5) { randomIndex = 6; }
             if (randomValue > 0.85) { randomIndex = Random.Range(7, 11); }
             if (randomValue > 0.5 && randomValue <= 0.85) {randomIndex = 0;} 
         }                                                                                                     // SECOND SET ends here
    }
  

• Code explanation:

This is a piece of code that's basically supposed to set randomIndex to a certain number with some probability, There are two sets of numbers (from 0 to 5 in first set and from 6 to 10 and 0 in second) it starts drawing in first set (because randomIndex initial value is 0) and if it happens to draw 5 from first set, then it goes to second set and draws numbers from 6 to 10 and 0, if it happens to draw zero it goes back to draw from first set and so on. The number that is drawn becomes randomIndex.

• Problem:

Code seems to ignore the second set. If it draws 5 in first sets it doesn't go to draw from the second but still moves around first. Even if I set randomIndex initial value to eg. 8 it still draws from first set only.