PSD of DWT details coefficnet

Hi,

I am working on a project involves sensor data analysis. I have a data for entire year that is sampled every 15 minutes. I used DWT (db4 up to three levels) to analyze the high-frequency content of the main signal.

After applying PSD on the reconstructed details signal, I can see some patterns between the levels, which I don't have a good explanations for them. According to the attached figure, level 3 has two cycles, level 2 one cycle, and level one half cycle. Why is that?

Also, as I remember DWT isolate frequency bands per each level, while there are some overlap in frequencies here. Is it due to the filter nature?

I really appreciate if you can give me your thoughts or suggestions.

Thank you in advance.