Can we limit parent in generateTreeList function?

Question

I am using Cakephp Tree Behaviour to list hierarchical data. Blow is the complete out put using generateTreeList function.

(
    [1] => Skoda
    [2] =>    Kushaq
    [3] =>    Taigun
    [4] => Maruti Suzuki
    [5] =>    Swift
    [9] =>       Swift VXI
    [11] =>          Swift VXI ABS
    [10] =>       Swift LXI
    [6] =>    Baleno
    [7] =>       Baleno RS
    [8] =>       Baleno LS
    [16] => Toyota
    [17] =>    Innova
    [18] =>    Landcruiser
)```


From this Skoda and Maruti Suzuki are parent categories. 
Is there any way to limit parent categories with their and get all the childrens?
Expecting result is like:

Array
(
    [1] => Skoda
    [2] =>    Kushaq
    [3] =>    Taigun
    [4] => Maruti Suzuki
    [5] =>    Swift
    [9] =>       Swift VXI
    [11] =>          Swift VXI ABS
    [10] =>       Swift LXI
    [6] =>    Baleno
    [7] =>       Baleno RS
    [8] =>       Baleno LS
)

Thanks in advance.Please help me to resolve this.