Usage of it and them with the same noun

Here is an example situation where the noun refers to something in general-

(General statement) The coconut tree is my favourite tree. It can grow up to a height of 25 meters.

(1) I used to climb them and pick their fruits.

(2) Although it is so tall, I used to climb it and pick its fruits.

(3) Although it is so tall, I used to climb them and pick their fruits.

(4) Although they are so tall, I used to climb them and pick their fruits.

I feel (3) is awkward and am not sure about (2). Can someone give some input and maybe an explanation?