Find lowest common ancestor of 2 nodes in a Binary Tree

Find_lca_btree.rb

def find_lca(val1, val2, root)
    stack = []
    stack.push [root, []]
    ancestor_list_val1 = []
    ancestor_list_val2 = []
    until stack.empty?
      t = stack.pop
      if t[0].data == val1
        ancestor_list_val1 = t[1]
      elsif t[0].data == val2
        ancestor_list_val2 = t[1]
      end
      break if !ancestor_list_val1.empty? && !ancestor_list_val2.empty?
      new_ancestor_list = t[1].unshift(t.data) # adds parent to start of ancestor list
      stack.push [t.right, new_ancestor_list]
      stack.push [t.left, new_ancestor_list]
    end

    if !ancestor_list_val1.empty? && !ancestor_list_val2.empty?
      return (ancestor_list_val1 & ancestor_list_val1)[0] # performs intersection of the 2 ancestor lists
    end
    nil
end