Write The Shortest Program to Calculate Height of a Binary Tree
Jelly, 3 bytes

ŒḊ’


A monadic Link accepting a list representing the tree: [root_value, left_tree, right_tree], where each of left_tree and right_tree are similar structures (empty if need be), which yields the height.

Try it online!

How?

Pretty trivial in Jelly:

ŒḊ’ - Link: list, as described above
ŒḊ  - depth
  ’ - decremented (since leaves are `[value, [], []]`)