How to handle the Nominal Data by Weka J48

When I ran J48 of weka with binary split option, such decision tree was built.

http://www.fastpic.jp/viewer.php?file=2693704973.jpg

Input explanation variable is 1 nominal data which was made by question id + answer id. 1 nominal data, 1 transaction. I'm wondering why the tree is at only one side.

Is it caused by my data set or table definition or original binary splits way? I'd like the tree to have node on both sides.

If you know such a option please show me.

!Sample Data! Please ignore dot '・'

• usr,qa,class
• A,11,1
• A,21,1
• A,31,1
• B,12,2
• B,22,2
• B,32,2
• C,13,3
• C,23,3
• C,33,3
• D,11,4
• D,22,4
• D,31,4
• E,11,1
• E,23,1
• E,31,1
• F,12,2
• F,22,2
• F,33,2
• G,13,3
• G,22,3
• G,32,3
• H,12,4
• H,21,4
• H,33,4

There's no error in the tree built and no option would really modify it. If your question is related to your same Akinator project, please reformat your data to get all questions (ie. 11,21,31) on the same instance/line and the answer as target class.

PS: if you import those data as CSV, Weka will take those data as numerical (not as as nominal). You should then add a non digit character (ie. #1,#2,#3...) so that Weka will take those data as nominal.