What does this sentence mean?
One can eat the fruit of that tree in spring or anything else?

What came to my mind first: someone drew a picture of a tree and shows it to you. Though, I'm not even fluent in English.

In this case, one doesn't have to say it because I can also see that a tree must be a tree in spring.

Hey maaster,

I'm not sure what your point is, are you looking for a context for this sentence?

The most obvious context to me is an adult describing a picture to a young child, but of course it can be used in other situations as well.

Sometimes I tend to think that a simply sentence surely means something more than it is.

Yes, this can be said e.g. by a child or by Jackson Pollock.

By a child or to a child :) Having two young children, I often describe obvious things to them. That's what they like and that's how they learn to understand and to speak :) And recently I had to explain seasons to the youngest one, so while I probably didn't say this sentence verbatim, I was definitely saying something rather similar.