I finally finished the tree shaped book shelf. However I made mine a little different.
I decided that 3 layers of 3/4″ plywood was not thick enough. Also if I made it thick enough for a book shelf it would be too heavy using all wood products. Also when I had the pattern laid out on the board I widened the base by about 1″ to 2″ and tapered it up the trunk. Made it look more like a tree. Had trouble finding carbon paper to trace the pattern on the board. Luckily a local wood worker had some on hand.
I started mine with a 1/2″ OSB board then alternating layers 2 ea. – 1″ styrofoam and 1 ea. – 1/4″ Luan for a total thickness of 7″. As for the Styrofoam I used it more to reduce weight than cost. However one sheet (4' x 8') of 1″ Styrofoam at Lowe's cost me $15.17 plus tax. Interesting note two 1″ Styrofoam cost less than one 2″. The 1/4″Luan was on sale at Home Depot. The OSB board was a scrap piece I had.
The edges are covered with vinyl speckling. I tried to seal the edges first with Durham's Rock Hard (water putty) but it set up too quickly and was very hard to hand sand. So I used Vinyl Speckling instead. It sands much better and does not set up quickly. Should let it dry overnight before sanding.
To mount it I had a local welding shop make me a bracket of a 1/4″ steel plate 2″x3″ with a 3/8″ round stock set at a 45 degree angle. I drilled a hole in the back of the tree at a 45 degree angle and chiseled a 1/4″ recess so the bracket would fit flush to the wall when mounted. Below are photos of the mounting bracket. The local machine shop charged me $5. for two of them. As it turns out I only needed one to mount the bookshelf because the weight rests on the floor. The hook only keeps it from tipping forward. The hook mounts to the wall at a stud location.