Absalom.
Bark covers a tree trunk.
The trunk of a tree is called a 'bole'.
the outer part of a tree trunk
Tree trunk is a compound word
the outer part of a tree trunk
Cellulose makes the trunk of a tree sturdy.
If 'hung it up on the tree' is in the past tense, as in 'He hung it up on the tree!', it is correct. If it is in the present tense, then, no, it is incorrect. In the present tense, the correct way of saying it would be, 'hang' or 'hangs', not 'hung'.
the outer part of a tree trunk
Is a wooden tree trunk a compound
Yes. A trunk is not only a stem but it is the main stem of a tree.
rain and winds
Cellulose makes the trunk of a tree sturdy.