Question

many other trees in this garden as tall as this into superlative degree

Answer 1

in this sentence, TALL--> tallest

Answer 2

Question: Many other trees in this garden are as tall as this . ( Positive)

Superlative:
Many other trees of this garden are tallest as this .

Its competitive :
Many other trees in this garden are taller than this .

HOPE IT WOULD HELP