The lower performance on TTL and FAC entities is likely due to the fact that the context patterns of TTL and FAC entities are similar to those of person and location names respectively, which makes them easily be regarded as special person names and location names respectively.
the whole MCTS algorithm looks like a tree structure (see Figure 2(b)), where the node s represents for known entities, i.e., both seed entities and previously extracted entities, and the edge,  (b) The Monte Carlo Tree Search for the pattern evaluation in a bootstrapping system for entity set expansion.