Maksim Rashchynski / Dennis Seah
Both of you have *Impeccable* knowledge and have your unique way of coding. Most of the folks in this forum are learning a lot from you. 
1. Now you got what you want, a button in tree header. 
2. And for your second point, you can have combination of layouts to achieve it.
3. For the third point, I used endButton aggregation of Dialog control in the sample, instead you can use buttons aggregation to have more number of buttons.
Regards,
Sai Vellanki.