I made two more branches today and I decided this was enough. Now I have to join them all together.
I cut a wire twice as long as my arm is, folded in the middle and hooked it to the lowest leaf of the smallest branch like this.
Then I twisted the wire around the rest of the branch until the end where I let it hang.
I added branches this way - I put the branch to the trunk and bent it.
I found out I had to twist it with a few (inner) wires from the trunk so that it was stable and didn't move.
I took the outer wires (at first they were two and as I was increasing they were finally six), tried to keep them in a flat line and twisted the tree.
Eventually I got this strange something between bush and tree with a big buch of wires sticking out.
The next step will be fastening to a piece of rock.