When Looney Labs rose from the ashes of IcehouseGames, they needed a lower cost product since they needed to work up to the production costs of the pyramids. Andy Looney came up with Fluxx, which became their flagship game.
In a lot of ways, Treehouse was meant to pull a similar trick.
Before treehouse, the primary way to get the pyramids was in colored caches of fifteen. Both Ice Towers and Zendo came in boxed sets but it was a lot easier to find the caches. The problem was that you needed multiple caches to play virtually anything and the caches themselves didn't come with any rules.
So if you wanted to get into the pyramids, you had to invest in multiple sets, along with digging up the rules. Mind you, that wasn't a problem for me. By the time treehouse came out, I have gotten every single color that was available and bought the Playing with Pyramids book of rules. But I am kind of crazy that way.
What Treehouse did was give you a low price entry point into the world of pyramids. You got fifteen pyramids divided into five colors (so you got one of each size in each color), a die and the rules to Treehouse. Instead of buying a bunch of parts, you bought a complete game.
Treehouse was a pretty simple game. Everyone got one trio of pyramids, with an extra one set in the middle in the treehouse formation. On you were turned, you would roll the die in the results would give you different ways of moving your own pyramids, with your goal to have your pyramids matching the treehouse.
(I wrote a review of the game shortly after it came out which describes the rules in greater detail: https://boardgamegeek.com/thread/121940/ever-changing-treehouse-icehouse)
Treehouse didn't just represent a new way to package the pyramids. It also showed a new philosophy for the game design. Before Treehouse, most of the pyramid games were pure abstracts. Treehouse is a quick, luck-filled little filler.
And, as near as I can tell, Treehouse did succeed at being a killer app for the pyramids. Treehouse is still in print after 10 years and has had several different editions. In general, I've seen the different forms of pyramids sold in more stores than I did back in 2006.
Compared to a number of other pyramid games, Volcano and Zendo in particular, Treehouse doesn't seem that strong to me. It really is just a little time filler with the die often forcing you to make choices you'd rather not make.
But... I have gotten a lot of games of Treehouse in over the years. 15 little plastic pier meds and one plastic guy makes for a game that you can carry in play just about anywhere. You don't have to worry about it getting wet or muddy so it's perfect for restaurants and coffee shops and picnics.
So maybe my inner game snob just to has to own up to the fact that it is a fun little game.
And there is no is no denying that Treehouse helped spread the pyramid system and helped make it more mainstream.