I made one similar to that because I was too cheap to shell out for the pre-made version and also because I like to give at least one homemade thing to my kids for most occasions.
I did scrimp on doing the bases by myself. I bought some pre-cut pieces of wood (maybe maple, this was years ago) at AC Moore. They still had the bark on the edges and were very nice. I raided a neighbor's yard trash pile by the road for some tough branches to hold up the different levels. Then I just screwed and glued them in after cutting them to equal heights. I skipped the staircase, but I did make a rope ladder with embroidery thread and twigs and I made a little hammock out of scrap fabric. The kids loved it for awhile and then they loved it a little too much and painted it and then one of the branches came loose I think. We've still got it, but it's a little worse for the wear at the this point, but I probably made it 3 or 4 years ago or so. It really came out pretty well at the time and I had fun doing it. Pretty cheap, too. All I paid for was those base slabs at the craft store.