[Pharo-dev] Why does not have a standard Tree Structure in Pharo?

Dear Pharoes, I see a lot of tree applications in Pharo, like Nautilus, GLM, FastTable, Spec, etc but they have their own tree structures. not common for others. I just looked into Dolpin Smalltalk , it has a standard TreeStructure class used anywhere. Why does not have a standard Tree Structure in Pharo? Best regards! Liang