How to replace some trees of certain type when growing?

I am wanting to make around 10% of trees grown by saplings be replaced with a structure block with a slightly modified tree inside


What I want to know is:


    

  1. How to detect when any sapling grows
    2. 

  2. How to use random chance
    3. 

  3. Use structure blocks in a datapack (I know how to use them, but unsure how it works into datapacks)
    4. 



Eventually I want this to work with world generation, but I figured saplings would be an easier place to start


P.S. I have no idea how events work, or how they trigger .mcfunctions (I was thinking of using a command to set the structure block)
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