I was trying to create a animated effect on the branch of the "Sapling tree gen" but couldn't animate the respective.So,I would like to know is there a way to animate just the "branch growth" property.If not then can you please give me an idea of how to accomplish the respective? Thanks in advance.
You can achieve a simplistic tree growth animation using the Bevel Factor property of the curve.
You might have to separate your tree into several discreet branch levels, and for a proper realistic effect it will probably require a lot of manual work.
Create a Sapling tree, enter Edit Mode select the whole main trunk and separate it with P.
Then select one of the branch tips (radius $0$), Shift+G Select Grouped > Radius then Ctrl+L to select all linked vertex. Press P again to separate that whole branch level.
Repeat for every branch level you wish to animate independently.
You can then animate the individual Bevel Factor properties on each curve object to achieve a simplistic growth animation by pressing keyframing the property with i while hovering it.
Separate into further objects for more detailed growth, for example by height levels, so lower branches can start growing before the upper ones.