It was Dogwood and imstr8 gave a very good answer.
The Bible does not state what kind of tree that it was made of. The story has been told that it was dogwood and repeated through time but this appears to be another legend or wise saying attributed the Bible but is not found anywhere in the Bible, similar to the saying " The Lord will not put more on you than you can bear".
It was made from dogwood
I have not seen any where in the bible that states the type of wood that was used so I'm with the guest whom answered wood, that we can be sure of that it was wood.....
The cross was made from dogwood then a very straight tree it is said after this the dogwood would never be used in cruifing again and was shortened and bent