How to combine/join/mergr two or more wavelet packets??

Hi friends,

Currently I work in wavelet packet decomposition (WPD) using EEG signals. The sampling frequency is 128 Hz. Based on the need I decomposed the EEG signals into four levels. As a result I got 16 sub-bands (24) packets. The focus was paced on four frequencies: f1: 1-4 HZ, f2: 4-8 Hz, f3:8-12, f4-f8:12-32 and f8-f16: 32-64. I got the wavelet coefficients for individual packets. But I would like to combine/merge/join the wavelet packets in order to obtain the frequency 12-32 Hz and 32-64 Hz. How to get these frequencies from wavelet packets??

Thanks in advance