Alone

When I saw the treetop, I knew I was close to the Ghostbusters' headquarter. That tree was very big[huge] and its roots were buried deeper into the earth. Its trunk was covered by a dark rough bark and there was no fruit at those branches. All the fruits were strewn/scattered/lying on the grass. I thought that in this way its seeds will be fertilised. The night was approaching fast; coming on, a dog was barking far away in the distance like a wolf and I was starting to feel a bit of fear. Can I say shit-scared and to be polite anyway? If you are describing the character as a lout etc, you can use this "scared shit" phrase.  It is very acceptable and even effective.  On the other hand, there is no polite way.  You can use other phrases or adjectives.  For example, "my blood began to curl...", "my heart goes a thump thump beat...", "terrifying", "trepidation" etc.

Alone

When I saw the treetop, I knew I was close to Ghostbusters' headquarters. That tree was very big and its roots were buried deeper in the earth. Its trunk was covered by a dark, rough bark and there was no fruit at on those branches. All its fruit was were on the grass. I thought that in this way its seeds will be fertilised. The night was coming on, a dog was barking far away like a wolf and I was starting to feel a bit of fear. Can I say shit-scared and to be polite anyway?

[Good work.  'Fruit' is considered uncountable, except if you are talking about different kinds of fruit.]