Well, it might be centered around spiritual growth. The 'sermon' in the guava tree could symbolize a moment of enlightenment or a deeper understanding of some sort of spiritual or moral truth. It could be that the character experiences a transformation while in the presence of the guava tree, leading to a change in their perspective on life and how they should live it.
I'm not sure without reading the story in full, but it could be a young person. Maybe a child or a teenager who is the one experiencing the sermon in the guava tree.
The main theme could be growth. The fig tree might symbolize growth, either of a character or of a situation in the story.
I think the main theme could be about survival. In many short stories, characters face various challenges and have to find ways to survive, and perhaps 'the fever tree short story' is no different.
The main theme might be about the significance of the banyan tree in a particular setting, perhaps it represents a place of memories, growth, or a connection to nature.
The main theme could be isolation. In the story, the characters might be isolated from society or from each other, creating a sense of loneliness.
The main theme could be about the fir tree's longing for something more in life. It might be about its desires and how they lead it through different experiences.
The main theme is sacrifice. The apple tree sacrifices itself for the boy's needs.
One possible theme is sacrifice. The flowering tree, being a living entity in the story, might have to endure certain hardships or make sacrifices. This could be paralleled with the experiences of the human characters in the story, where they also face situations where they have to give up something for a greater good or for the sake of others.
One possible main theme could be the cycle of life. Just as the apple tree goes through seasons, from budding in spring to bearing fruit in fall and then being bare in winter, it can mirror the life cycle of the characters in the story.
The main theme could be about the power of suppressed anger and how it can grow into something toxic. It shows how holding onto negative emotions can have harmful consequences.