i want to create a button in potree web that imports las/laz file from local and render it on scene
Remember that the whole thing about rendering millions of points has to do with using a spatial partitioning system. For this it is required to process and format the original point cloud into an octree-based representation. Potree provides this pre-processing step by using its PotreeConverter to generate an octree-complaint version of the original point cloud, that a potree viewer can latter on consume.
You can see in the LAS Potree example that the point cloud is referenced as a simple object indexing each of the octree leafes/childrens.
Also keep in mind to post further questions on the potree issues page.