Alternative splicing is an important process in gene expression. Alternative Splicing can lead to mutations and diseases. Most studies detect alternatively spliced genes with ESTs (Expressed Sequence Tags). However, reliance on ESTs might have some weaknesses in predicting alternative splicing. ESTs have been stored in the libraries. The EST libraries are often not clearly organized and annotated. We can pick erroneous ESTs. It is also difficult to predict whether or not alternative splicing exists for those genes where ESTs are not available. To address these issues and to improve the quality of detection and prediction for alternative splicing, we propose the One-leaf One-node Tree Algorithm that uses pre-mRNAs. It is achieved by codons, three nucleotides, as attributes for each chromosome in Arabidopsis thaliana. The proposed decision tree shows that alternative and normal splicing have different splicing patterns according to triplet nucleotides in each chromosome. Based on the patterns, alternative splicing of unlabeled genes can also be predicted.