Frequency of CHH, CHG methylation in Comparison to CPG

Question

[gtasource]

I'm working with Bisulfite sequencing data. Looking at the results, I am seeing high prevalence across the board for CHH and CHG sites. My biology isn't the greatest, so could anybody either explain or provide some literature about the prevalence of these methylation patterns? I'm using CGMap to list the coordinates.

Appreciate the help!