Take a close look at the tree in the immediate foreground. About two-thirds of the way up the tree. The tree has done a magnificent job of growing around the branch that has become wedged between what, presumably, used to be two separate parts of the tree. Either that or there was a very strong gust of wind one day that impaled the tree 
Related posts:
- Orchid on fig tree root After leaving Faint’s Mine, and crossing a deep, dry creek...
- Growing on nothing Back into gorge country today above the Macleay River, and...
- Fabulous fungus: Orange platelets Tiny orange fungi growing on a small, rotting tree branch...
- Lightning-blasted tree I was introduced to this tree on a ridge in...
- Epiphyte When walking in Oxley Wild Rivers National Park last weekend...
Very cool picture. I’m not sure if either theory is the right one..
We had a pear tree in the garden that years ago someone had put a mole trap in a fork of the tree and forgotten it. Over the years, the tree had grown around the trap and it was deeply embedded. We still have moles!!
Maybe your tree had a split in it and someone shoved the branch through and then the tree continued to grow around it.