"There is sugar in my tea."
Both sentences are valid in terms of meanings. I would like to briefly go through each of them before sharing one of mine.
我的茶里有糖 is literally "My tea has sugar". 里 expands the description of the sentence, but this doesn't make a difference from the English sentence kokaku mentioned.
我的茶里加了糖 is literally "My tea inside added sugar", which makes "My tea is added with sugar". This includes more feeling and touch of vocabularies than the previous sentence.
I can also find another way to express more prosy sentences, such as 我的茶有加糖, which indicates that the sugar is already added. Instead of including 里, 有加糖 is another way to indicate that something is "being sugared". This type of sentence is more used by native speakers than three previous sentences.