The Tree of Zaqqum is some of the food that the people of Hell will eat from. The Tree of Zaqqum is so awful, if a drop of Zaqqum was to be placed on this Earth, everything on Earth will be ruined. Can you imagine then how horrible it is to have it as food?
"Without doubt, the Tree of Zaqqum, will be the food of the Sinful. Like murky oil, it boils within bellies, like the boiling of scalding water." Qur’an.Surah Dukhan 44:43-46
Such food will also cause the person to suffocate. A very clear description can be found in Surah Saffat: " Is Paradise a better accommodation or the tree of zaqqum? Indeed, We have made it a torment for the wrongdoers. Indeed, it is a tree issuing from the bottom of the Hellfire, Its emerging fruit as if it was heads of the devils." Qur’an.Surah Saffat 37:62-65 
Narrated by Ibn `Abbas(R): Regarding: 'And We granted the vision (Ascension to the Heaven "Miraj") which We showed you (O Muhammad as an actual eye witness) but as a trial for mankind.' (17.60) It was an actual eyewitness which was shown to Allah's Messenger (S) during the night he was taken on a journey (through the heavens). And the cursed tree is the tree of Az-Zaqqum (a bitter pungent tree which grows at the bottom of Hell). Sahih Bhukari Vol. 6: 240 and Vol 5:228 
This is the tree to which Allah likens the believer because it is good in all aspects, it is lasting and it offers different kinds of benefit. Ibn ‘Umar reported: "The Prophet (May Allah Honour him and Grant him Peace) said: ‘There is a kind of tree whose leaves do not fall and it is like the Muslim. Tell me what it is.’ The people mentioned different kinds of desert trees … and I said to myself, ‘It is the date palm tree,’ but I felt too shy to speak up. Then the people said, ‘Tell us what it is, O Messenger of Allah.’ He said: ‘It is the date palm tree.’" (al-Bukhari, 60)
By the fig and the olive. Qur’an surah 95:1
Abu Asid said: "The Prophet (May Allah Honour him and Grant him Peace) said: "Eat the oil and use it on your hair and skin, for it comes from a blessed tree." (Reported by al-Tirmidhi, 1775; see also Sahih al-Jami’)
"And indeed he (Muhammad saw him (Jibril) at a second descent (i.e., another time), near Sidrat al-Muntaha (the lote tree of the utmost boundary, beyond which none can pass), near it is the Paradise of Abode, when that covered the lote-tree which did cover it! The sight (of Prophet Muhammad (peace and blessings be upon him)) turned not aside (right or left), nor did it transgress beyond (the) limit (ordained for it). Indeed, he did see of the Greatest Signs of his Lord (Allah)." [al-Najm 53:13-18]
In the famous Hadith about his Mi’raj (ascent into heaven), the Prophet (May Allah Honour him and Grant him Peace) said that when Jibril took him up into the heavens, he went through from one heaven to the next by the command of Allah, until he reached the seventh heaven. He said: "Then I was taken to Sidrat al-Muntaha; its fruits were like the pitchers of Hajar and its leaves were like the ears of elephants. He said, ‘This is Sidrat al-Muntaha’…" (Reported by al-Bukhari, 3598).
Abu Hurairah (may Allah be pleased with him) narrated that the Prophet (May Allah Honour him and Grant him Peace) said: "In Paradise there is a tree in whose shade a rider could travel for a hundred years without crossing it. Recite, if you wish: ‘In shade long-extended’ [al-Waqi’ah 56:30]" (Reported by al-Bukhari, 4502)
Allah says (interpretation of the meaning): "And O Adam! Dwell you and your wife in Paradise, and eat thereof as you both wish, but approach not this tree, otherwise you both will be of the Dhalimin (unjust and wrong-doers)." [al-A’raf 7:19]
Abu Hurairah said: "The Messenger of Allah (May Allah Honour him and Grant him Peace) said: ‘The example of the believer is like that of a plant which is continually bent over by the wind; the believer is continually beset with afflictions. The example of a hypocrite is like that of the cedar tree, which does not yield until it is uprooted in one go." (Sahi Muslim, 5024)