Indeed it is a tree grown up from the bottom of the Hades.
When it is mentioned that the Zakhoom tree grows from the bottom of Hell, the wrongdoers mock it. Thus, the warning of verse 6: 10, which says, “Whatever punishment the disbelievers were ridiculing, it happened to be true upon them,” applies to these wrongdoers. That is why the Zakhoom tree is a Trial for the wrongdoers. The believer has confirmed belief that the Almighty Lord, who is capable of everything, can also produce a tree from the bottom of fire, just as He could convert the fire into peace and coolness in the case of Messenger Ibrahim, as mentioned in verse 21: 69. The Fujjar, who are also disbelievers, do not use Adhikr here as the Safeguard against Hellfire, so they will end up in Hell in the seventh phase, as mentioned in verses 5: 10, 86, and 82: 14. See explanation 4: 140, 145; 36: 80-82.