Well, this is the tree I made last weekend. This is a complex design, but it's easy to do if you have in your mind the image of the tree finished.

You must cut some tabs because they are there to glue each part of the design as you prefer.

If you can, use cardboard to strengthen the big parts of the model (the 5x5 blocks base) and put something hard and heavy en log's base

(Note: the upper block is a separated one)