signal analysis – Approximating an FFT using a DWPT

I’m a telecommunications engineering PhD student at UNSW in Sydney.
I am attempting to use a discrete wavelet packet transform to decode some signals using variable time and frequency support.
As a general test, I am trying to approximate an FFT of a length 64 example signal x cos(2pit5) + sin(2pit13), using a discrete wavelet packet transform, the dwpt() function in MATLAB. However, when I perform the wavelet packet transform at level 6 on the signal, I am getting amplitude peaks at normalised frequencies of 10 and 26 Hz, double the frequencies appearing in the FFT. I understand that MATLAB’s dwpt samples from 0 to F/2, which would explain the doubling of the frequencies, but how is it that if the time support of the sampled frequency bands is the same as the FFT, the bandwidth can be halved? Does this not violate the uncertainty principle?

Please let me know if I am completely wrong and have a misunderstanding
Thanks
Hamish