It’s difficult to understand what you actually mean by ‘opinion’? It’s a vague and vast question. But to give you an answer in short, here it is — 
 
The poem ‘The Heart of the Tree’ is a very simple and short poem which tells us about the benefits of planting tree and the greatness of a tree planter. Divided into three stanzas of nine lines each, the poem describes how trees beautify nature and keeps the ecological balance, how trees are important for the safety of our future generation and how trees can lead to a nation’s growth.
 
Though it essentially deals with the importance of trees, it pretends to be more concerned with the man who plants a tree by repeating the line “What does he plant who plants a tree? at the beginning of every stanza”. And that has been a great technique to inspire the readers to plant more and more trees. 
 
Though the poet’s main concern is with the themes, the poem is rich in its use of figures of speech and other poetic devices. And most importantly, the poem, though written over a century ago, is very relevant in our time when rapid and reckless urbanisation is taking its toll on the Environment.