Learning about trees is usually teached in high level algorithmic and data organization courses.
If possible I will give specific pointers to the most online texts that were of the most use for me
For this topic I ended up in my own homecountry for the best text;-). Get the postscript files
310,311 and 312 and you know almost every basic thing, including proofs and pseudocode
Because it is always nice to have some cross validation for this kind of topics I can advice
another online source too.In this case you are advised to download lectures starting from 9 with all graphics!.