Should be quite easy..
First Node (Status Check):
Lvl 10 and below: Make one Check Status, Choose Status needed "Level". Then under comparisation choose IsLess and then put the value to 11.
Link the success node connection to the rest of the formula and then link the failed to the next status check node below.
Second Node (Status Check)
Lvl 11-20... same steps as above just that you put the value to 21
Third Node (Status Check)
Lvl 21-30..... same as above.... but a value of 31 I think you got what I mean now ;)
This means that he will check if the character is lvl 1-10 first, if a success then he continues with the formula you have for that level. If not within this level bracket then it will return a failure which will leads to the next status check node that will check if the character is below lvl 21 which in practise means that he will check lvl 11 to 20 since he already tried 1-10 in the node above.
/T