is it possible to make an block that, when placed, will grow a tree where it was placed?

Yes. To do this, you will need a tree structure(assuming that you are making a custom tree), and a plant. Make this plant force-tick- it should be found in the Properties of the plant- and make a trigger that happens on "Update tick." Then, go into the Template Library- it's at the top right of the menu, looks like a stack of papers- and pick the "Do with a 70% chance" option. Change the 0.7 to a 0.1, and then(this might just be because I use the Snapshots of MCreator) put inside of the thingy a "Place at X Y Z with rotation NONE mirror: NONE structure:" and put in the tree structure(I'm not going to explain how to upload structures, you figure that out yourself) in the slot. Hooray! Tree!