By Ibnul Qayyim (r.a)
The year is a tree, the months are its branches, the days are its twigs, the hours (and minutes) are its leaves and every breath man takes is a fruit of the tree. Thus the fruit of the trees of a person who breathes in obedience to Allah will be sweet and the fruit of the tree of a person who breathes in disobedience to Allah will be bitter. However, the fruit of this tree will only be harvested on the Day of Ma’aad (the day when Man will return to Allah) and the sweet fruit will only be differentiated from the bitter fruit when it will be harvested.
Ikhlaas and Tauheed are a tree in the heart (of the Believer). The branches of this tree are good actions and its fruits are a pleasant life in the world and never-ending comfort in the Hereafter and just as the fruit of Jannah will never come to an end nor will it be held back, the same can be said regarding the fruits of Ikhlaas and Tauheed in the Dunyaa.
Shirk, lies and Riyaa (doing good actions for show) are also a tree in the heart. The worldly fruits of the tree are fear, worry, sorrow, narrowness of the heart (discontent, cowardice, etc) and darkness of the heart. In the Hereafter the fruits of this tree will be Zaqqoom and everlasting punishment.
These two trees have been mentioned by Allah in the following Aayaat of Surah Ibrahim:
“Did you not see how Allah presented an example? A pleasant word is like a pleasant tree; its roots are firm and its branches are (high) in the sky, it yields its fruit all the time with the command of its Sustainer. And Allah presents examples to the people so that they may take heed. And the example of a bad word is that of a bad tree that has been uprooted from above the earth having no firmness.” (Verse 24 – 26)
Source: Jameah Mahmoodiyah