Four words, and almost nothing happens. Someone looks at a tree and notices it is hazy. There is no setting, no story, and no stated feeling. The poem simply holds one moment of looking.
What stands out is the grammar. The line has no "the" or "a" in front of "tree," so it feels less like a sentence someone composed and more like a thought arriving as it is seen. The word "so" adds a small note of surprise, as if the speaker is half-amazed at how much the tree has blurred. We can't tell whether the haze is mist, heat, distance, or tired eyes, and the poem doesn't settle it.
The mood is quiet, soft, and a little dreamy. The tree's edges seem to dissolve, and the reader is left with that same uncertainty, looking at something that won't quite come into focus. The poem's brevity makes you slow down and notice the blur yourself.