Analysis of The Shepherd's Tree

Huge elm, with rifted trunk all notched and scarred,
Like to a warrior's destiny! I love
To stretch me often on thy shadowed sward,
And hear the laugh of summer leaves above;
Or on thy buttressed roots to sit, and lean
In careless attitude, and there reflect
On times and deeds and darings that have been -
Old castaways, now swallowed in neglect, -
While thou art towering in thy strength of heart,
Stirring the soul to vain imaginings
In which life's sordid being hath no part.
The wind of that eternal ditty sings,
Humming of future things, that burn the mind
To leave some fragment of itself behind.