Explanation of Leaf Value of plot_tree method

Can anyone explain me what behind calculation of that leaf value in plot_tree method?
Im already watch explaination math details in youtube, but i got different result what covered in video and code in python im already try,

is leaf value is a prediction residual from model?

Take a look at my master’s thesis: https://drive.google.com/file/d/0B0c0MbnP6Nn-eUNRRkVOOGpkbFk/view. It explains how the leaf value is computed.

Thanks u so much sir, i’ll read it :slightly_smiling_face: