I hate trees..

[Chris2Balls [:B]]

give it more character.

this looks like a pretty old tree considering its size; old trees tend to be pretty firmly rooted in the ground, and life tends to spread around it- insects, birds, plants, fungi that grow on or next to the tree... when a tree reaches that size, it starts to define its surroundings.
your tree seems to lack branches, and i find it very unlikely that a tree has such a wide branch (eg the one on the left).

the tree has an entrance: this gives it a function. why is there a hole in the tree? what is it for? where does it go? where is this? what season and time is it? there are quite a few other questions you could ask yourself to make this piece progress, but it's up to you to question yourself and answer these.

good luck!