It may appear to you to be the case, but DeepBlue used a tree search algorithm. AlphaGo was an ensemble method that was based on neural networks, just like how the researchers used to detect sarcasm (sequence to vector). Read the article!
Every tree search algorithm needs a guiding heuristic, and that's what AlphaGo replaces with a neural network.
So both DeepBlue and AlphaGo are fairly described as being based on tree search.