This paper focuses on the ability of robots to summarize long-term experiences and answer questions—that is, to verbalize robot experience. While previous studies have limited generalization and transferability by applying rule-based systems or fine-tuned deep models to short-term experience data, this study leverages a pre-trained, large-scale language model to verbalize a robot's lifetime experience through zero- or few-shot learning. It generates hierarchical tree-structured data from episodic memories (EMs), representing raw sensory and proprioceptive data at low levels and abstracted events using natural language concepts at high levels. The large-scale language model acts as an agent to interactively explore the EMs based on user queries, dynamically expanding tree nodes to find relevant information. This approach maintains low computational costs even with months of robot experience data. We evaluate the flexibility and scalability of our method using simulated home robot data, human-viewpoint videos, and real-world robot recordings.