And We made not the vision which We showed you (O Muḥammad [pbuh] as an actual eye-witness and not as a dream on the night of Al-Isrā) , but a trial for mankind... (V.17:60)

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 (ﷺ) 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).