case 1:
   tree input: 10 5 15
   1.1. delete 10
   1.2. delete 5
   1.3. delete 15

case 2:
   tree input: 10 5 4 3 
   2.1. delete 5
   2.2. delete 4

case 3:
   tree input: 20 10 5 15 6 25 24 30 29 
   3.1. delete 10
   3.2. delete 25

case 4:
   tree input: 20 10 5 15 8 7 25 24 32 29 30
   4.1. delete 10
   4.1. delete 25