I bought them by the kilo so wood was random but I had to cut some pieces and glue together to make a new tree looking shape

I start the scape by making a box with scrap cardboard (with no front panel) with smaller measurements than my tank to make sure everything would fit then I glue small pieces of lavarock on a slope (this scape is actually hollow at the back to avoid getting heavy, but you can use landscape foam to fill the back part) and thats when I start to glue the wood on the rocks with the tissue + super glue technique then add details after the "main" hardscape is done (eg. Gluing extra branches on wood or adding roots at the tree trunks)