In just four short lines, the speaker sees an oak tree that stands alone and old, and the sight sends him back to his father's bedside. The poem never says why he is there or what happened, but the jump from tree to bed suggests the memory arrives all at once, the way real memories often do. The oak's loneliness and age seem to mirror the father, who may have been frail, ill, or near the end of his life. That is an inference from the imagery, not something the poem states.
The phrase "I place myself back" is interesting. It sounds deliberate, as if the speaker chooses to return rather than simply being pulled there. Maybe he wants to stay close to his father, even if the memory hurts. The mood is quiet, still, and sad, with a kind of solemn tenderness. The short lines and plain words leave a lot of silence around them, which lets the feeling settle without being explained.